Ma a C a P 256 (2020) 123706

A a ab 25 A 2020

0254-0584/ 2020 E B.V. A .

Cu 2 addition and sintering temperature dependence of structura microstructura and die ectric properties of CaCu i 2 ceramics

afar oumc edda C aouc i as ue e edda ra imi a faoui ououdina

Researc Unit ateria s r cesses an n ir n ent UR ac t ec n Uni ersit a e ara er es eria a rat r ie e istr an e ica n ineerin a eri Uni ersit i i eria

Unit na ics an tr ct re ec ar ateria s Uni ersit itt ra te a e a ais rance Researc enter in n stria ec n ies R era a iers eria

e art ent sics e e cience Uni ersit a rain a rain

irst or on t e s nt esis of CaCu i using Cu instead Cu

ig densi cation increase in grain si e and en anced cr sta init it sintering temperature

eduction of densit of acant Cu posts in CC usefu for en ancing t e densit t roug t e i uid p ase Cu Cu Cu ased CC ceramics e i it e ce ent die ectric properties at o fre uenc ma ing t em suita e for capacitors

C

e r s Ceramics CC

o der meta urg and ie ectric properties

C

is stud is aimed in t e rep acement of common used Cu Cu2 in t e s nt esis of pero s ite CaCu i 2 CC p ase t e so id state reaction met od e ana sis of po der ca cined at C and ceramics sintered at different temperatures s o t at t e CC p ase as e cr sta i ed it t e presence of sma uantities of additiona p ases e ana sis of prepared pe ets s o t at t e for mation of Cu2 Cu p ase occurs a o e C resu ting in en anced densi cation at C

o e er it is found t at t e Cu2 ased CC egins to degrade around C e densi cation after sintering at C reac es mean i e die ectric constant and oss tangent a ues are optimum in t e o fre uenc range i e and respecti e is fa ors t e use of Cu2 instead of Cu in CC ceramics for app ications at o fre uencies

1. Introdu t on

e searc for no e die ectric materia s it ig e ectrica prop erties associated it sma o umes remains c a enging ince t e 2 s t e ig die ectric constant a ues ere o ser ed in o ides Cu i 2 ere represents a di a ent cation suc as Cd Ca and r is c ass of compounds cr sta i es in cu ic pero s ite t pe structure 2 e most promising ceramic contains ca cium CaCu

i 2 a so no n as CC is ceramic is among t e materia s a ing a co ossa die ectric constant r 2 at f in t e temper ature range of and o oss tangent tg at f

un et a reported as o a ue as tg at and room temperature dditiona CC does not e i it a ferroe ectric e a ior ing to a o e remar a e properties CC is eing considered as a er promising materia for app ication in microe ec tronics suc as die ectric p anar antennas capacitors or micro a e de ices CC can e i it non inear current o tage e a ior resu ting from c ott arriers at grain oundaries s C ung et a reported t at t e non inear coef cient of CaCu i 2 reac ed a a ue of ic is e en greater t an t at of t e aristor materia n s a resu t CaCu i 2 ma ead to ef cient s itc ing and gas sensing de ices e s nt esis of t e CC p ase is genera carried

Corresponding aut or Corresponding aut or

ai a resses r d afar uni oumerdes d afar m oudina gmai com ououdina Contents ists a ai a e at cience irect

ateria s C emistr and sics

ttps doi org matc emp s 2 2 2

ecei ed arc 2 2 ecei ed in re ised form une 2 2 ccepted ugust 2 2

out t e con entiona met od so id state reaction using ca cium car onate CaC copper o ide Cu and titanium o ide i 2

uring t e s nt esis t e c oice of Ca Cu and i precursors as a great importance ndeed t is factor affects t e p ase formation and composition t e e o ution of partic e morp o og and si e ic in turns a e a direct in uence on t e p sica properties t as found t at t e gro t of t e grains during sintering is in uenced t e amount of e cess Cu in t e ca cined po der o e er ang c ang ia et a noted t at secondar p ase partic es i 2 Ca i remained as so id state partic es ic ere inso u e in t is state and t at t e grain gro t rate is in i ited so id i 2 partic es e impro ement of die ectric properties of CC ceramics is o tained after optimi ation of t e uantit of different p ases of t e materia o e er u ramanian et a noted t at t e die ectric properties of CaCu i 2 p ase are affected t e accurac of Cu Ca ratio e non o mic properties of CC ceramics can e impro ed t e samp e treatment in o gen ric atmosp eres and increasing t e mo ar ratio of i from t e stoic iometric a ue of CaCu i 2 2

arious aut ors reported t e in uence of copper o ide Cu on t e die ectric properties of CC e copper o ide or cupric o ide it t e formu a Cu is often used to prepare CC

e ert e ess anot er p ase Cu2 Copper o ide or cuprous o ide can a so e used to prepare CC Cu2 is ric er in Cu compared to Cu f Cu is rep aced Cu2 t e densit of acant Cu posts in Cu s ou d e signi cant reduced ic eads to a good densi cation t roug t e formation of i uid p ase of Cu2 Cu

n t is researc or t e preparation of t e CC ceramic t e traditiona so id state reaction met od using Cu2 instead of Cu is reported n particu ar t e in uence of Cu2 on t e e o ution of structure and p ase composition partic e morp o og and die ectric properties of CC ceramics is in estigated i e ar ing t e sinter ing ca cination temperature e main goa t erefore is to stud and e a uate t e e tent of rep acing Cu Cu2 and t e corresponding modi cations in structura and p sica properties

. r nt ro dur

CC ceramic po der as s nt esi ed from stoic iometric amounts

of CaC Cu2 and i 2 ioc em C e

mop arma Compan t e so id state reaction met od

irst t e po ders starting materia s ere mi ed and mi ed in et ano igma dric using a p anetar mi

C it irconia media at 2 rpm for fter dr ing in an e ectric o en at C for t e mi ture as ca cined in t e air at

C for e ca cined po der as manua ground in an agate mortar for 2 min t en re mi ed for 2 again in t e same a mi using r 2 a s to e iminate t e agg omerates t en unia ia pressed using a manua operated drau ic press into pe ets it a diameter of mm and t ic ness of 2 mm at a pressure of 2 pa for s using ioc em C emop arma Compan as inder t na step t e pe ets ere separated and sintered at and C for and t erefore t e samp es CC CC and CC

appeared respecti e e optimi ed ca cination temperature is found to e C since t e po ders ca cined at temperatures e o not presented in t is or s o t e presence of secondar p ases at ig e e e samp es sintered at temperatures of C and a o e not s o n in t is or ere fused or deformed en iang uan et a 2 suggested t at momentari eating t e reactants to C is an essentia step in comp eting t e so id state reactions e aut ors per formed simi ar ca cination at C and t e sintering temperature

C as e o t e ca cination temperature

e cr sta ine structure as c aracteri ed ra diffraction using an i ips e uipped it Cu radiation source it a step si e counting time 2 s and s eep ang e e microstructure as o ser ed scanning e ectron microscop coup ed it energ dispersi e

ra spectroscop using a emini em eiss at an acce eration o tage of or t e e ectrica c aracteri ation t e sintered pe ets ere po is ed to ac ie e uniform para e surfaces and t en t e si er paint as app ied on ot surfaces of t e sintered dis s and red at

C for min e die ectric measurements ere performed in t e fre uenc range from 2 to using an C meter

. u t nd d u on

tr ct ra ana sis R ase r ati n

e pattern of po der ca cined at C is s o n in ig a e e de ned and re ati e road pea s are o ser ed indicating ig cr sta init of t e samp e t e pea s can e inde ed it in a od centered cu ic cc pero s ite t pe structure in t e space group

o 2 in agreement it t e pattern reported in t e iterature and C card num er 2 for CaCu i 2 o minor pea s are identi ed and attri uted to t e presence of sma amounts of i 2 and Cu p ases erein it is important to ig ig t t at t e appearance of ne p ase Cu is due to t e o idation of Cu2 at ig temperature as reported in t e iterature 2 22 e densities of sintered pe ets ere measured rc imede met od e densit of CC CC and CC dis s as measured to e and g cm

ic correspond to and re ati e densit respecti e considering t e t eoretica densit of g cm for CC 2

e e o ution of t e patterns of CC pe ets as a function of sintering temperature is presented in ig s in t e ca cined sam p e e de ned pea s are o ser ed i e t e re ati e intensit en ances due to etter cr sta init associated it grain gro t and ig er c emica omogeneit t e ma or diffraction pea s of CC CC and CC matc it t ose of cu ic CC

e o intensit additiona pea s a so appear and t e are attri uted to minor p ases of Ca i Cu i2 and iC e identi cation of i2

and iC pea s as con rmed a spectrum ana sis it t e ig core us soft are in agreement it t e C cards n for iC and C n for i2 using t e C 2 data ase C 2 e ease 2 e i2 and iC p ases on appear en t e sintering temperature reac es C e appearance of Ca i CaC Cu iC and i2 indicate t e partia decomposition of CC ean i e it is important to note t at t e intensit of Cu main pea increases ic means t e increase of its amount it t e rise of sintering temperature

e densit of t e sintered samp es as measured rc imede met od 2 t as found to e greater t an of t eoretica densit for a t e ceramics prepared in t is stud CC ecomes unsta e in t e air at ig temperature and partia decomposition occurs at C to CaC Cu and i 2 2 it is a so noted t at ot er p ases ma appear during t e decomposition process in iang et a 2 reported t at t e gradua segregation and o ati i ation of Cu Cu2 is e pected et een and C efore comp ete degradation to Ca i and i 2 at C e temperatures corresponding to decomposition or formation of CC pro a decreases to some e tent

n addition a ea pea around 2 can sti e seen in t e pattern of a simp es corresponding to t e meta ic Cu indicating t e reduction of Cu² to Cu meta

icr str ct ra ara eters

e a erage cr sta ite si e of CC as ca cu ated e e c errer met od 2 using formu a t is noted t at t is formu a neg ects t e strain effect to ca cu ate t e cr sta ite si e n order to o tain a more accurate a ue of cr sta ite si e t e i iamson a met od 2 2 as proposed to estimate t e microstructura parame ters cr sta ite si e and microstrain using formu a 2 n addition t e ce parameter of t e cu ic CC attice is ca cu ated from t e

C 256 (2020) 123706

position of t e o ser ed diffraction ines in t e pattern according to re ation 2 e a ues of cr sta ite si e attice micro strain and ce parameter ca cu ated e e c errer and i iamson a p ot met ods are gi en in a e

2

ere is t e cr sta ite si e is t e a e engt of Cu radiation is t e diffraction ang e is t e fu idt at a f ma imum

denotes t e microstrain a is t e ce parameter of cu ic attice and and are t e i er indices of t e considered ragg re ection

e cr sta ite si e a ues ca cu ated t e e e c errer met od are a itt e it ig er t an t ose o tained t e i iamson a s met od e o ser ed s ig t difference is it in accepta e range e cr sta ite si e considera increases it increasing t e sintering temperature due to grain gro t in agreement it iterature ei Cao et a used a disso ution precipitation sintering d namic mode to

e p ain t is e o ution in cr sta ite si e t as reported t at it t e sintering temperature increase from to C sma grains gradua me t and precipitate on t e outer surfaces of t e arge grains to ecome t e secondar grain oundar p ases pon furt er increase in t e sintering temperature up to C t e secondar p ases at grain oundaries continue to me t and are a sor ed t e arge grains ean i e it is important to note t at as t e sintering temperature increases t e microstrain decreases as associated to t e attice re ation upon annea ing upp et a 2 reported t at in nanocr sta ine ce ramics it progressing t erma treatment t e microstrain decreases due to atom ordering in t e cr sta attice and reduction of t e con centration of stac ing fau ts and point defects e ca cu ated ce parameter are in agreement it t at reported in t e iterature

erein it is important to ig ig t t at t e s ig t s ift of t e 22 re ection suggests t e o ser ed s ig t c ange in t e ce parameter i e a s ift to ig er 2 indicates a decrease in ce parameter and contraction of t e unitce i e a s ift to o er 2 is associated it an increase of ce parameter and unit ce e pansion s reported in a e and ig t e CC ce parameter increases en t e sintering temperature increases to and C i e surprising a contraction of t e unit ce is o ser ed at C e mec anism of attice e pansion contraction in CC is not et c ear understood it depends on t e t pe concentration and nature of arious intrinsic defects created under different gro t and sintering conditions is c ange in attice . 1. patterns of t e specimens a ca cined at C and sintered at arious temperatures

1

Cr sta ite si e attice parameter microstrain and cr sta init of pseudo pero s ite CC cu ic sintered at arious temperatures intering emperature

C

Cr sta ite si e e e c errer nm

Cr sta ite si e i iamson a nm

icrostrain attice parameter a osition of 22 pea

Cr sta init

eference 2

2 2

2 2 2

2 2

R a ar et a

parameter and attice strain ma e o ing to t e incorporation su stitution disp acement and segregation of sma amount of atoms into from t e attice dams et a reported t at a reduction of Cu² to Cu occurs at suc ig temperatures C it c arge compensation partia occupation of Cu site i so a partia reduction of i to i as suggested and it is associated it t e o gen oss o gen acancies from t e attice n addition it ma e due to t e segregation of Cu from CC attice Cu acancies to form Cu ric inter granu ar a ers as reported in t e iterature 2 s an et a 2 reported at ig er s nt esis temperature t e oss of Cu ta es p ace due to Cu segregation or o ati i ation is ma e compensated partia o idation of Cu² to Cu e ionic radius of Cu is sma er t an t at of Cu² ic ma e t e reason for t e ce parameter decrease at ig er temperature

r sta init

e effect of sintering temperature on cr sta init is determined from t e ratio of t e areas t e integra of t e diffracted intensit of t e cr sta ine pea s to t e tota area of pattern according to t e fo o ing re ations ip

e ca cu ated a ues of cr sta init are gi en in a e e pea s are s arp and narro it re ati e ig intensit signif ing t at t e sintered CC samp es are of ig ua it it good cr sta init e atter is found to gradua en ance it t e sintering temperature

ic is in agreement it t e resu ts reported ang et a r ica ser ati ns

e micrograp s recorded for CC po der ca cined at C are s o n in ig 2 t can e seen t at agg omerates of grains are formed indicating t at t e pre sintering as occurred during ca cina tion e grains are fair regu ar and are different in si e e partic e si e ranges from to m e po der partic es are aggregated pro a due to moisture adsorption caused storage conditions n omogeneous microstructure it a imoda grain si e distri ution

can e seen in t e po ders n ig a series of images is gi en for t e surface morp o og of ceramics sintered at different temperatures s s o n in ig a a arge porosit is o ser ed in t e pe et sintered at C it a imoda grain si e distri ution i a narro grain si e distri ution of 2 m for t e dot in u grain red dots ii arge grains of si e ranging et een and 2 m for t e dot in u grain e o and ue dots iii and u tra ne grains of a out 2 nm as o ser ed in t e oomed se ected red one ig a2

fter sintering at C ig and C ig c a ne and dense microstructure of t e CC is o tained ndeed t e grains of t e pe ets are in t e range 2 2 m in diameter for t e pe et sintered at C ig 2 and m in diameter for t e pe et sintered at C ig c2 ean i e t e morp o og signi cant c anges it t e sintering temperature it transforms from sma er and irregu ar s aped grains to arge and irregu ar s ape

e ana sis of pe ets pro ides more e idence for t e segrega tion of Cu2 Cu p ase and it gi es more information on t e ones ric in Cu ccording to t e data ot eig t and atomic percentages o tained for Cu are gi en for eac samp e t can e ig ig ted t at t e sintering temperature of C as not reac ed t e point ere t e Cu Cu2 p ase ecomes i uid ic eads to partia and imited sintering ig a and e spectrum for t e samp e sintered at C ig c re ea s t o ma or pea s corresponding to and i it t o minor pea s corresponding to Ca and Cu t e corresponding c emica composition inset a e indicates 2 at of Cu is in fact e p ains t e o densit of t e samp e sintered at t is temperature compared to t e samp es sintered at C ndeed a Cu ric p ase starts to segregate out of t e ceramic at C and it accumu ates et een t e CC grains as an inter granu ar p ase as indicated spot 2 on ig a and spot on ig d e atomic percentage o tained for Cu in t e u grain ig c and in grain

oundar ig of t e rst section is found as 2 and at respecti e or t e second section t e atomic percentage o tained for Cu in t e u grain ig e and in grain oundar ig f is found as and 2 at respecti e e Cu content in grain oundar is found to e ig er t an t at in u grain for ot sections ic indicates c ear t at t is one is ric er in Cu and Cu is one of t e most ide used additi e to promote densi cation i uid p ase sintering

. . images of CC po der ca cined at C

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resu ting in ig er densi cation en t e temperature rises up to C t e Cu p ase egins to o ati i e and a t in a er appears on t e pe et surface ig a and t e corresponding atomic percentage o tained for Cu is ig c e densit decrease of t e pe et sintered at t is temperature is t erefore e p ained t e oss of Cu e presence of additiona pea s corre sponding to i C i and in t e ana sis is due to unintentiona contamination from t e mi ing media used during t e po der pro cessing or iC a rasi e paper during po is ing of specimen

ectrica r erties

e die ectric constant and t e die ectric oss tangent a ues of t e ceramics samp es sintered at different temperatures and measured at room temperature and in t e fre uenc range from 2 to are gi en in ig e a ues o tained at o fre uencies 2 are isted in a e 2

e die ectric constant a ues ar in t e range o er a ide fre uenc range from ² to e oss tangent a ues range it in e rea part of t e permitti it rapid decreases as fre uenc increases CC possesses t e o est die ectric constant a ue t disp a s a uite ig oss tangent a ue at o fre

uenc ic ecomes o er t an a o e is

important span of t e oss tangent ma signif an important imitation

for app ications or CC medium a ues of t e die ectric con stant associated it oss tangent a ues c ose to 2 are measured

or CC t e ig est a ues of t e die ectric constant are ac ie ed at o fre uenc ut t e die ectric constant a ue continuous decreases do n to at e oss tangent p ot as seen in ig s o s a continuous increase unti a ma imum reac ed around fter t is pea t e oss tangent a ue decreases to at is particu ar e o ution of t e die ectric properties et us t in to a die ectric re a ation or con rming t is assumption e a e p otted t e e o ution of t e osses imaginar part of t e die ectric permitti it in ig

s seen in ig CC effecti e s o s a magni cent domain of re a ation centered at f is ind of die ectric re a ation domain is genera associated at t is fre uenc it a a e agner effect o t is p enomenon cou d e in re ation it t e disp acement and accumu ation of e ectrica c arges t at modi es t e die ectric properties of t e ceramic sintered at C ere of t e ceramic sintered at C is domain is t erefore pro a due to an e trinsic effect and not to t e intrinsic properties of CC

ctua t e e ectric c arges can e accumu ated at different p aces of t e samp e suc as arge grain oundaries or areas ere t e meta ic e ectrode is not in contact it t e u ceramic causing space c arge effects at o fre uenc genera ca ed a e agner effect . . images for arious ceramics sintered at different temperatures for a and a2 C and 2 C c and c2 C R a ar et a

o it is important to remind t at t e die ectric properties of ceramics are strong re ated toman factors inc uding ceramic microstructure suc as a erage grain si e and pe et densit t e p ase a undance p ase structure parameters suc as cr sta ite si e and attice strain processing conditions inc uding sintering temperature and coo ing rate and preparation of t e samp es for e ectrica measurements or t e pe et sintered at C t e ana sis s o s t e presence of t e main p ase of CC it a o content of Cu and re ati e ig cr sta init of e o ser ation of images s o s t at t e Cu2 Cu p ase ic fa ors sintering in t e i uid p ase cannot form at t is temperature ic imits t e densi cation process and grain gro t 2 nm n addition it eeps a certain porosit t ere resu ting in o er die ectric constant a ues associated

it ig er osses en t e sintering temperature rises to C t e amount of Cu p ase increases as con rmed ana sis

oreo er t is temperature is suf cient for Cu Cu2 p ases to e formed and t e segregation of Cu atoms egins to ards t e grain oundaries resu ting in grain gro t from 2 to 2 2 nm a reduction in porosit and etter densi cation as re ea ed images e cr sta init increases to 2 as e dense microstructure is effecti e ad antageous for impro ing e ectrica properties 2

e as impro ed properties of t e pe et sintered at C e i it ig a ues of die ectric constant at o fre uenc ut t is a ue uic decreases ere due to a a e agner e trinsic effect or t e pe et sintered at ig er temperature of C t e ana sis re

ea s t e disappearance of some pea s of CC p ase and appearance of ne p ases suc as iC Ca i Cu and i2 indicating t e degra dation of CC p ase a ong it t e segregation and o ati i ation of

Cu forming t in a ers on t e samp e surface as e idenced ana sis t is found t at t is ig temperature promotes grain gro t

2 2 nm and en anced cr sta init ut it a so acce erates and increases t e segregation and o ati i ation of Cu ea ing pores in t e ceramic microstructure ic e p ains t e drop in densit

e degradation of CC p ase and t e densit decrease ead to a decrease of die ectric constant a ue

ina from t e ana sis of o tained resu ts t e sintering temper ature of C can e considered as t e most appropriate for CC ceramics e a orated at t e conditions presented ere oreo er t is materia ma pa e t e a for t e use of Cu2 ased CC in t e de e oped ceramic capacitors

. u on

Compared it t e iterature t e signi cant resu ts o tained in t is stud can e ig ig ted as fo o i t e main p ase formed is CC

it t e presence of er sma uantities of minor p ases ic is in agreement it some pre ious studies in iterature ii t e o tained a ues of grain si e densit and die ectric constant are ig er t an t ose reported u et a as s o n in a e i e narro grain si e distri ution of m after sintering at C for it a densit of a out and die ectric constant in t e range of espite t e ig sintering temperature C for a ong time uang et a o tained a o er densit of a out and er o a ues of 2 angc ang ia et a reported road grain si e distri ution in t e range of m after sintering at C for and ig a ues of after treatment at C for . . ana sis of t e ceramics sintered at C for a and images and c spectrum it t e corresponding c emica composition

C 256 (2020) 123706

. . ana sis of t e ceramics sintered at C for a and images and c e and f spectra it t e corresponding c emica composition

R a ar et a

it t e use of Cu in an e cess i e ang et a o tained a ig er densit of muc arger grain si e around m and a ues t at do not e ceed t e a ue of and it is o er compared to t e a ues o tained in t is stud t is important to ig ig t t at in t is stud for uite o sintering temperature and s ort time energ gain t e grain si e and die ectric properties can e tuned up to maintaining ig er

densit a ues e g for sintering at and C for t e grain si e aries from to m it ig a ues in t e range e as o tained resu ts are more signi cant compared to t ose o ser ed a man et a and esurani et a t s ou d e noted t at ig grain si e a ue is re uired in t e de e opment of CC C mode ereas ig er densit a ue is recommended to a e etter die ectric properties rom t e e o comparison a e it can e ig ig ted t at no simi ar stud on t e de e opment of Cu2 ased CC s as een so far reported in t e iterature and it t ere pa es t e a for furt er researc es to e a uate and impro e t e die ectric properties of Cu2 ased CaCu i 2 ceramic compos ites ome c aracteristics of t e as prepared CC s stem are gi en in

a e in comparison it simi ar s stems in t e iterature in terms of c emica composition ca cination and sintering temperature it t e corresponding modi cations of structura p ase formation . . ana sis of t e ceramics sintered at C for a and images and c spectrum it t e corresponding c emica composition

. . o ution of t e a die ectric constant and die ectric oss tangent of CC ceramics sintered at different temperatures in function of fre uenc

e die ectric constant and t e die ectric oss tangent a ues of t e pe ets sin tered at different temperatures measured at room temperature and at f 2

intering temperature C tg

2

C 256 (2020) 123706

microstructura cr sta ite grain si e porosit and densit and su se uent t e e o ution of t e die ectric properties rom t e resu ts reported in a e t e fo o ing points can e ig ig ted

i e addition of 2 of r i to CC it Cu impro ed densit a o e i e drastica deteriorates t e die ectric constant a ue from 2 for pure CC do n to after t e addition of r i e samp es are mi ed p ases and consist of CC and r i e o ser ed c anges in die ectric constant a e een e p ained ic tenec er s oga rit mic a

ii e effect of sintering time at C it different soa ing times 2 on CC it Cu s stem is in estigated t is noted t at t e densit of CC ceramic s ig t increased at ig er o ding time o e er t is a ue sti remains o and does not e ceed accompanied it o die ectric constant a ues i e in t e range 2 for and muc o er at ig er fre uenc i e for e o die ectric prop erties can e attri uted to morp o og porosit and o grain si e t ma e a so associated it t e ind of sintering met od used in t is or ic eads to an important s rin age a ue

2 2 for of soa ing time

iii e effect of ca cination conditions on ot t e microstructure and die ectric proprieties of CC ceramics prepared so ge met od as a so in estigated e grain si e increases it increasing ca cination time and temperature ut remains o er t an m er o tan a ues are measured i e 22 and 2 for CC 2 and CC respecti e associated to t e me dian a ues of die ectric constant of 2 and respec ti e n addition o die ectric constant for CC 2

as een ac ie ed for and muc o er for e o a ues can e attri uted to t e presence of impurit p ases in t e ca cined po der t at as a signi cant in uence on t e microstructure of sintered pe ets ic s o s a arge amount of pores as reported in t is or

i e die ectric properties densi cation and discontinuous grain gro t of CC ased Cu during t e sintering process are c ose re ated to t e Cu stoic iometr good densi cation

and a medium a ue of die ectric constant are o tained for t e CC pe et t oug t e pore gro t re ated to t e densit decrease is a so o ious for CC t s ou d a so e noted t at t e die ectric constant a ue for CC 2

is signi cant reduced 2 and it is associated to t e o er densit ic can e ascri ed to t e fact t at t e domains are not e de e oped inside t e ne grains 2 m

e su stitution of r 2 on t e i site as in estigated 2 e die ectric oss tangent remains e o o er t e fre uenc range of i e t e permitti it as reduced a factor of 2 as compared to t at of undoped CaCu i 2 e grain si e is constant at a out m independent of r 2 content is means t at t e degradation of t e die ectric properties of undoped CaCu i 2 is apparent not corre ated it t e c ange in t e cr sta structure or micro structure is degradation in die ectric constant can e attri uted to t e fact t at t e r 2 addition induces a modi cation in t e defect e ui i rium as reported atterson et a 2 i CC it Cu is prepared using con entiona so id state reac

tion re ati e o a ues of die ectric constant at room temperature are measured i e for and muc o er and 2 for and respecti e n t is or se era parameters grain si e densit ere not studied ic ma es it dif cu t for understanding t e origin of o die ectric constant a ues e die ectric constant of CC can e corre

ated it grain si e and t ic ness of grain oundar as reported i et a

ii e formation of CC it Cu s stem s o s t e e is tence of unreacted ra materia s and secondar p ases of i 2

Cu Ca i and Cu i due to t e o ca cination temperature C and uncomp eted ca cination process e samp es sin tered at arious temperatures are not fu dense and e i it a

o re ati e densit and ig porosit i e 2 and 2 for t e samp es sintered at 2 C C and C respecti e e a erage grain si e increases from m for 2 C to m for C i e t ere is an a norma gro t of grain si e o ser ed and a ot of porous areas i e of porosit at 2 C e porosit decreases at ig er sintering temperatures i e 2 and for sintering at and C respecti e ese microstructura c aracteristics a e a strong in uence on t e die ectric properties t e ig est a ue of die ectric constant measured at is o tained at s

C and t e o est a ue of die ectric constant is reac ed at

s 2 C

ii e die ectric constant of pure CC it Cu is a most constant t roug t e o e fre uenc range it a o er re ati e die ectric constant a ue or r doped CC t e a ues of t e die ectric constant are ig er t an t at of pure CC in t e o fre uenc range i e 22 and for 2 2 and of r respecti e e a ues of t e die ectric constant are e en o er in t e ig fre uenc range i e

at e ig est a ue of die ectric constant is en t e concentration of r reac es is a ue drops from

at f to 2 at e grains are found to e in t e si e range of 2 nm m ic can e e p ained comparati e o sintering temperature C and s ort sintering time min in a micro a e furnace ic eads to o die ectric constant e interna arrier a er capacitor C mode as ide accepted as t e most i e mec anism to consider t e re ations et een grain si e and t e die ectric constant

. on u on

is stud as de oted to t e e a oration and c aracteri ations of ca cium titanate and copper titanate ceramics CaCu i 2 CC fa ricated it t e addition of Cu2 instead of Cu

t as found t at after ca cination t e e cr sta i ed nano cr sta ine CC p ase it t e presence of minor p ases as suc cessfu s nt esi ed po ders ere produced t e so id state . . o ution of t e die ectric osses of CC ceramics sintered at different

temperatures in function of fre uenc

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reaction e ceramics sintered at and C a e o er re ati e permitti it a ues it uite ig osses erein it is important to ig ig t t at t e temperature of C as insuf cient for t e occurrence of Cu2 Cu p ase transformation eading to incomp ete sintering i e t e temperature of C is too ig ecause t e CC egan to degrade nteresting t e ana sis s o n t at a comp ete sintering as ac ie ed at an optimum temperature of

C it a ig densi cation rate dditiona CC e i ited t e ig est die ectric constant a ues at o fre uenc

and uite o die ectric osses tg is ceramic a so s o n a re a ation domain centered at f ic is due to a a e agner effect is e trinsic effect t at strong modi es t e e o ution of die ectric properties does not et us see t e rea e a ior of t e CC ceramic sintered at C e ert e ess considering t e e o ution of ot er CC ceramics and die ectric constant a ues measured at i e e o t e re a ation domain e ma suppose t at t e CC ceramic sintered at C is a e to gi e er interesting

die ectric properties or t ese reasons t e integration of CC ce ramics cou d e er promising for t e de e opment of o fre uenc ceramic capacitors

d ut or ontr ut on t t nt

. r a idation n estigation esources riting origina draft riting re ie editing isua i ation orma ana sis .

ou dd Conceptua i ation et odo og esources riting origina draft riting re ie editing isua i ation uper ision .

ou uper ision esources riting origina draft . u uper ision riting origina draft . dd esources .

r esources . ou esources . ououd n a ida

tion riting origina draft riting re ie editing isua i ation uper ision

ase composition grain si e densit and die ectric properties of t e as prepared CC s stem in comparison it simi ar s stems in t e iterature

reparation Conditions Cr sta ine p ases rain i e

m

ensit ie ectric roperties eference

CaC i Cu Ca cination at C

intered at C C C

CC Cu Cu Ca i i i

2 2 2

is stud

2 2

2 CaC i Cu

Ca cination at C for sintered at C for

CC

CC 2 r i

CC r i

CC r i ot

studied 2

CaC i Cu sintered at C for different soa ing times

oa ing time 2 oa ing time oa ing time oa ing time

CC ot studied 2

2

ot studied

2 2 2

so ge met od ca cination at

C for 2 CC C for CC 2 C for CC

pe ets sintered at C for

CC i Cu ot

studied

22 2

2

CaC i Cu

Ca cination at C for 2 sintered at C for

CC 2 CC

CC i Cu CaC 2 2 ot

studied 2 ot

studied

CaC i Cu r

Ca cination at C for 2 intered at C for CC pure

it r it r it r

2

2

CaC i Cu

sintered at C for

ot studied ot studied ot

studied

2 CaC i Cu

ca cined at C for 2 sintered at 2 C for sintered at C for sintered at C for

CC i Cu Cu i

Ca i 2 2

2

ot

studied ot studied

so ge met od

ca cined at C for

sintered at C for min in a micro a e furnace

CC pure

CC doped 2 r CC doped r CC doped 2 r

CC doped r

CC doped r

CC 2 ot

studied

2

2 2 2 2

2

2

C 256 (2020) 123706 r t on o o t n nt r t

e aut ors dec are t at t e a e no no n competing nancia interests or persona re ations ips t at cou d a e appeared to in uence t e or reported in t is paper

r n

u ramanian i uan eisner eig t ig die ectric constant in Cu i 2 and Cu i e 2 p ases o id tate C em 2

2 2

2 e eaton Co en ander i t C omes irst princip es stud of t e structure and attice die ectric response of CaCu i 2 s e 2 2

2 2

un u in tructure properties and impedance spectroscop of CaCu i 2 ceramics prepared so ge process m Ceram oc 2 C un iu in C g uan ei ang o temperature speci c eat stud of giant die ectric constant materia s s Condens atter 2 2 2 2

amire u ramanian arde um erg i ogt apiro iant die ectric constant response in a copper titanate o id tate Commun

2 2 22

angc ang ia atsitang ong ai initsoontorn am ong aensiri morn it amrung C indaprasirt u er o oss tangent and ig die ectric permitti it in pure CaCu i 2 ceramics prepared a modi ed so ge process m Ceram oc 2 2

ao iu a reparation c aracteri ation and die ectric properties of CaCu i 2 ceramics Ceram nt 2 2 22 22

C ung im ang trong non inear current o tage e a iour in pero s ite deri ati e ca cium copper titanate at ater 2

ar ier C Com ettes ui emet ritsc C artier ossigno umeau e e utarde CaCu i 2 ceramics from co precipitation met od die ectric properties of pe ets and t ic ms ur Ceram oc 2

2

u ramanian eig t Cu i 2 and Cu u 2 pero s ites ig die ectric constants and a ence degenerac o id tate ci 2 2

ang i C en ue ang e non o mic and die ectric e a ior e o ution of CaCu i 2 after eat treatments in o gen ric atmosp ere ater

ci ng 2 2 2

2 in Cai i C an ig die ectric and non inear e ectrica e a iors in i 2 ric Ca Cu i 2 ceramics pp s ett 2

2 2

u o amed in mad ffect of Cu cess on t e icrostructure and icro a e ie ectric roperties of CaCu i 2 Ceramics d anced ateria s esearc rans ec u 2 pp

i C en u u ang ffect of grain si e and Cu ric p ase on t e e ectric properties of CaCu i 2 ceramics ater ci 2

meida ec ine oes a ente iranda om ra ie ectric properties of a i CaCu i 2 CC composite screen printed t ic ms for ig die ectric constant de ices in t e medium fre uenc

range ater ci ng 2 2

u iu ao uo Cao ie ectric properties of CaCu i 2 ceramics modi ed r i ater ett 2 2

mara C u inger enr Costa a ente arros immons ie ectric properties of po st rene CC composite on Cr st o ids

2 2 22

ore an a a a ari ffect of a r i doping on die ectric properties of CaCu i 2 CC ater ci ec no 2 2 2 ang ou Cao i i mpact of Cu2 doping on ig die ectric properties of Cu ceramics Curr pp s 2

2 uana ar a ei ffecti e s nt esis to fa ricate a giant die ectric constant materia CaCu i 2 ia so id state reactions Ceram

rocess es 2

2 u imura ss i i idation mec anism of Cu 2 to Cu at C id eta s 2 2 2 222

22 ar ee o ar on o ana C oe ano ire i e copper o ide gro n on porous copper a promising anode materia for it ium ion

atter or C em oc 2 2

2 i ue ao ue C en e effect of ca cining temperatures on t e p ase purit and e ectric properties of CaCu i 2 ceramics o s Compd

2 2 2

2 ro er r an ie i a ures iggins ana is easuring sing e ce densit roc at cad ci 2

2

2 ang ei o ffects of Cu stoic iometr on t e microstructures arrier a er structures e ectrica conduction die ectric responses and sta i it of CaCu i 2 cta ater 2 2 2

2 e uo u in Cu segregation and its effects on t e e ectrica properties of ca cium copper titanate ci C ina ec no ci 2

2 2

2 madipour u a man in mad ssessment of cr sta ite si e and strain of CaCu i 2 prepared ia con entiona so id state reaction icro ano ett 2

2 ur o use C emistr etermination of t e partic e si es microstrains and degree of in omogeneit in nanostructured materia s from ra diffraction data ass s C em 2 2 2 2

2 upp nfortuna auc er icrostrain and se f imited grain gro t in nanocr sta ine ceria ceramics cta ater 2 2

Cao iu ou ang u C iu ang Ca cination and sintering effects on t e microstructure and die ectric properties of CaCu i 2 ceramics Ceram rocess es 2

dams C inc air est ecomposition reactions in CaCu i 2 ceramics m Ceram oc 2 2 2

2 an ang uan ao C iu iu reparation of giant die ectric CaCu i 2 ceramics ia t e mo ten sa t met od from aC u nt pp Ceram ec no 2 2

urt inor enera procedure for e a uating amorp ous scattering and cr sta init from ra diffraction scans of semicr sta ine po mers o mer C ang in 2 ao C C en C eng Compounds

icrostructura and e ectrica properties of Ca i CaCu i 2 ceramics o s Compd 2 2

er ing er ic t e gner ang ammer Copper o ide as a sintering agent for arium titanate ased ceramics ater ci 2

2

as ap is ra a ur andon tructura die ectric properties and e ectrica conduction e a iour of su stituted CaCu i 2 ceramics Ceram

nt 2 2

uang iang u CC giant die ectric ceramic prepared reaction sintering rocedia ng 2 2

ang ei o ffects of Cu stoic iometr on t e microstructures arrier a er structures e ectrica conduction die ectric responses and sta i it of CaCu i 2 cta ater 2 2 2

a man utaga ung mad in o amed C aracteri ation of microstructures e o ution on e ectrica responses of CaCu i 2 ceramics ing aud ni ng ci 2 2 2 2

esurani anagesan as im smai apis a n uence of oping on t e icrostructura and ie ectric roperties of icro a e intered Ca cium Copper itanate er arma C emica 2

ee a antas am C o dari a aratnam stimation of permitti it of a compact cr sta die ectric measurements on its po der a stoc astic mi ture mode for t e po der die ectric s pp s

2 atterson on C C uang Cann ffects of r 2 additions on t e die ectric properties of CaCu i 2 pp s ett 2 2

ri asta a nt esis and c aracteri ation of ig die ectric constant materia CaCu i 2 iomed ci ec nica es 2

C inc air dams orrison est CaCu i 2 one step interna arrier a er capacitor pp s ett 2 2 2 2

C iode i assarotti Capsoni ini C oni o ati upotto ectric and die ectric properties of pure and doped CaCu i 2 pero s ite materia s o id tate Commun 2 2 2 2

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