ESR STUDIES ON STEREOCHEMISTRY OF THALLOUS ION IN OXIDE GLASSES

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ESR STUDIES ON STEREOCHEMISTRY OF THALLOUS ION IN OXIDE GLASSES

H. Hosono, Y. Abe, H. Kawazoe

To cite this version:

H. Hosono, Y. Abe, H. Kawazoe. ESR STUDIES ON STEREOCHEMISTRY OF THALLOUS ION IN OXIDE GLASSES. Journal de Physique Colloques, 1982, 43 (C9), pp.C9-159-C9-163.

�10.1051/jphyscol:1982930�. �jpa-00222459�

ESR STUDIES ON STEREOCHEMISTRY OF THALLOUS ION

I N

OXIDE GLASSES

H. ~ o s o n o * , Y . be * and H. ~ a w a z o e * ~

"Department o f Inorganic Materials, Nagoya I n s t i t u t e o f Technology, Gokiso, Showa-ku, Nagoya 466, Japan

*'Department o f I n d u s t r i a l Chemistry, Faculty of Technology, Tokyo Metropolitan University, Fukasawa, Setagaya-ku, Tokyo 158, Japan

@sum&- La st6rhhimie de T1 dans une grande2yari6t6 de verres d'oxydes +

a

Bt6 Blucid6e par analyse des spectres

WE

du T1 paramgn6ticrue induit

par

irradiation

y

utilisant une nouvelle+solution de llHamiltonien de spin.

On

a trouv6 deux types

de

cmrdinence: T1 ayec un chaw

2

sym6trie quasi-sphgrique du c h m des ligandes (cmrd.

I)

et T1 ayant

un

champ de liqandes pyramidal (11).

Cette demisre cmrdinence s'est r6v6lGe dans les verres

03

coexistent des oxygsnes pntants et non-pntants.

Le

centre ~ 1 prcduit ~ +

2

partir de la cmrdinence

I1 a

relax6 en un centre semblable

2

celui r6sultant de

I

p r recuit des 6chantillon.s irradigs. Un &Sle structural cpi suppose un dEplacement de l'ion alcalin a 6t6 props6

s w

la base de l'anlyse

de

la cingtique de cette conversion.

Abstract.- The stereochemistry of TI+ in a wide variety of oxide glasses has been elucidated by analyzing

ESR spectra of y-induced paramagnetic ~ 1 2 +

employing a newly developed solution to the spin-Hamiltonian. It has been found that there exist two types of the coordination, T1+ with a nearly spherical-symmetric ligand field(coordination I) and TI+ having

a

pyramidal ligand field(I1). The latter coordination has ppeared in the glasses where bridging and non-bridging oxygen coexist. The TlzY center produced from coordination I1 has relaxed into the center similar to that from coordination I on thermal annealing of as-irradiated specimens.

A structural model involving the displacement of alkali ion has been proposed on the basis of the kinetical analysis of the conversion.

1.Introduction.- Thallous ion is the key component of manufacturing optical waveguide with gradient index because of its large polarizability originating from the electronic configuration(6s2).

However, detailed information on the stereochemistry of T1+ in glass has never been obtained.

We have succeeded in clarifying this problem by a plying ESR:

The thallous ion is converted into paramagnetic T12'(6s1], trapping aholein its lone pair orbital upon y-irradiation. The geometry of the precursor is preserved in the product if the ESR measurements of the samples irradiated at 77K are carried out without an intervening warm-up. Therefore, the stereochemical information on TI+ can be obtained from the detailed spin-Hamiltonian analysis and close line shape simulation of the spectrum of T12+.

2.Theory.-(i) Solution to the spin-Hamiltonian with axial hyperfine a n d n s o r s (~=1=1/2)

A theory was developed agpropriate for analyzing ESR spectra

characterized by 3C

= i 3 . H . g . S +

I S , where I=S=1/2, the magnitude of the latter term is greater than and/or comparable to that of the former, and both z-and r-tensors have axial symmetric character.

C a l c u l a t e d e n e r g y l e v e l s , e i g e n f u n c t i o n s a n d t h e c h a r a c t e r i s t i c s o f t h e e x p e c t e d t r a n s i t i o n s w e r e d e r i v e d a n d s u m m a r i z e d i n o u r p r e v i o u s p a p e r

K T 7

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982930

JOURNAL DE PHYSIQUE

Coordination

1

Coordination

I 1

Center

I 1

4

Fig.] Coordination of

T1

and v-induced paramagnetic

~ 1 ~ '

(ii) L i n e s h a p e s i m u l a t i o n

I n g e n e r a l , t h e r e e x i s t s a c o n t i n u o u s l y r a n d o m v a r i a t i o n i n l o c a l s t r u c t u r e s f o r t h e s t a t i s t i c a l e n s e m b l e o f t h e c e n t e r of i n t e r e s t i n glass. T h i s v a r i a t i o n r e s u l t s i n a c o n t i n u o u s v a r i a t i o n of t h e r e s p e c - t i v e H a m i l t o n i a n p a r a m e t e r s . I n p r i n c i p l e , a l l t h e r e l e v a n t p a r a m e t e r s f l u c t u a t e , but w e i n t r o d u c e d o n l y t h e d i s t r i b u t i o n of t h e i s o t r o p i c c o m p o n e n t ( A i s o ) of t h e A - t e n s o r t o s i m u l a t e t h e e x p e r i m e n t a l s p e c t -

rum closely. This assumption

had been found to be sufficient

<"7%a

for the centers with large Aiso

[2-41. Then, the line shape function,S(H), for ~ 1 ~ ' is given in eq.1;

Flp+e 2 ^{The ESR} spcba of in xNa,D3T120(97 - x)Sii2 (lasses

where i,I,f and H denote the

(x. m o ~ %): (a) x = 12. (b) x = 17, (c) x = 27. (d) x = 47. The doned

observable trans it ion, trans it i on

^{line IS h} line shape of TI2+ In 10T1,0.90B,O, glass'0 (v = 9.2 W ) .

probability, convolution function and magnetic field, respectively.

P(Aiso)

function is of a the distribution Aiso.

Detailed - -E-

^{, n}

^{_ ...}

^{: . .... b}

simulation procedures were

_-..< . i. .:*.

...-...

^" ,...--- ^{.LIL C}

described in our preceding

^.-,

paperL51 .

_? ^L _{I I I I}

Z d e can be classified into two types[6]: One has a nearly spherical ligand field

(coordination I), which is usually seen in ionic crystals containing TI+. The other has a pyramidal

geometry(I1). The T 1 - 0 bond in the former is of lower covalency (weaker) and that in the latter is of higher(stronger1. On exposure to y-rays at

_{7 7 K ,}

a TI+ having each coordination is c nverted into a paramagnetic TIP+ as shown in Fig.1.

Figure 3 Expenmental and calcubted ESR ltne shapes 01 the TI2* a s i g ~ l (I! = 9.2 GHz). (a) exoer~mental sgecbum of 7K,Q3Tl,O90SiO, glass (the b-a- of h @ s i b 1 that is present is indicited i n ' h figwe by -1; (b) computed powder panern using the spin-Hapiiionian pa- rameters listed in Table III: (c) computed line shape assuming a Gaussian-type distribution with a = 0.06 cm-' for .A,

Figure 4 Experimental and calculated ESR itne shape of the TI'+ 0

signal (u = 9.2 GHz): (a) experimental spectrum of 49KN03.

lTlN0,~50Ca(N0,)2 glass: (b) computed line shape using ihe ESR parameters listed in Table I 1 and the Gaussian distribution wim tr =

0.40 cm-' for A.,

participates to a large extent.

a signal p signal

The MO in center

11

is composed

matrices 7K,0.3T1,0.90Si02 49KNO;1TINa0,-

of the T1 6s-6p(-5d) hybridized a

^{50Ca(NO, ),}

orbital.

^{gu= 1.9515 giso = 2.000}

g l =-2.0286

Figure 2 shows the ESR spectra

-X A = 1.6965 c ~ - ' A ~ , , = 3.9364 c ~ - '

of ~ 1 ~ ' in Na20-Si02 glasses.

^{B = 1.6561 cm-'}

~ ~ i r o ~0.060 cm-' 0.400 cm"

These signals can be regarded as

own,c 30 G 30 G

a superposition of the spectra

s characterd 27.2% 64.2%

from two kinds of the center, a -

p characterd 32.0% -

and 6-signals. The least over-

a The glass batch was melted in a quartz glass tube under

lapping a-and 6-signals were

degassing.

*

^The Gaussian distribution for the isotropic

obtained in 7K20.3T120v90Si02

hf coupling (Ai,) was introduced in order to fit the ex-

perimental line shape closely. oi, is the standard devia-

and the nitrate glasses(Figs.3

tion of A~,,. Convolution was made by using a Gaussian

and 4). Table 1 shows the

function with the standard deviation o,,,,. a'Atomic

extracted ESR parameters through ~ ~ . a ~ ~ ~ ~ : 6 d ; : i ~ ~ ~ ~ ~ ~ ~ ~ ~ i ~ ~ A f ~ ~ ( 6 s ) =

^6,1309

the computer simulation of each spectrum. On the basis of

the MO coefficients listed,

Table 2 Correlation between the coordination of

it is concluded that the

a- TI* and the composition of host glasses

and 6 -signal have to be

assigned to center

11

and

TI~+ESR OXYGEN TYPE

I, respectively.

SYSTEM COMPOSITION a B B . 0 N.B.0

The correlation Was

extensively investigated

Na20 - Si02 o o

o o between the coordination

and the chemical composi-

^{SILICATE N a ~ O} _{SiOZ (Na/Al=l)} ^{-A1203 - X 0 0} x

tion of host glasses.

BaO -Si02 0 0 0 0

A s

summarized in table 2,

it was found that the a-

GERMANATE

INa201K20

x o o x

signal(i.e,coordination 11)

20g,[Na201

o

o

o o is seen in the glasses in

which both bridging and

[Na,0]<25 0 o x

non-bridging oxygen coexist,

B ~ R A ~ E 25&?~a~01<55

o

o

o while the

B

is observed

_{5 5 s [NaZO] 2 o x} ⁰

for the glasses where only

⁰

one type of the oxygen

PHOSPHATE 50Na20-50P205 0 0 0 0

is present.

SULFATE ZnSOq-K2S04 X 0 x 0

4.Structural relaxation of

as-induced ~ 1 ~ ' upon

NITRATE KN03-Ca(N03)2 x 0 x ⁰

annealing.- On annealing

B.O:brldglng oxygen, N.B.0 non-bridglng oxygen,

of as-irradiated specimens

0 :observed (exist), x . not observed(not exist)

at a temperature- higher

than - 8 0 ° c , the a- signal relaxed to the

6

as exhibited i n Fig. 5. T h i s c o n v e r s i o n w a s n o t observed i n alkali-free glasses. Two facts above men- tioned suggest that the

a+B

conversion r a t e is c o n t ~ o l l e d by a displa- cement of alkali ions as illustrated i n Fig. 7. To confirm the m o d e l , analysis of the conversion k i n e t i c s w a s attempted. T h e alkali ion pai- ring w i t h as-induced ~ 1 ~ intervening a nonbridging oxygen is conside- ' red to be repeled f r o m its original position to other available sites in order to relax the repulsion due to a n excess plus charge o n the

~ 1 ~ ' . T h u s , the conversion should be spontaneous (i.e, first order)

reaction if following the model. The site-to-site fluctuation in T1 coordination in g l a s s e s , w h i c h is proved b y the existence of distribution o f the s p i n Hamiltonian p a r a m e t e r , gives r i s e to the distribution of the r e l a x a t i o n t i m e T . T h e r e f o r e , we employed the fractional exponential form w h i c h i s the superposition of many simple exponential decays /7/

i n analyzing the data (Fig. 6) ;

JOURNAL DE PHYSIQUE

w h e r e I(Io) is the intensity of the a-signal after (before) t i m e t of annealing and u is a parameter expressing the d i s t r i b u t i o n w i d t h of T.

As n o change i n the line s h a p e of the a-signal w a s found during the warm-up, the 1 / 1 0 is equivalent to hlh,, ( h and h o are inscribed in Fig. 5). F i g u r e 8 exhibits Arrehenius plots for the c o n v e r s i o n process.

The activation energy w a s estimated t o b e 9.8 kcallmol. T h i s v a l u e i s compatible with t h e activation energy for alkali d i f f u s i o n process such a s electric conduction. T h e r e f o r e , the analysis of the c o n v e r s i o n k i - netics substantiates the model illustrated in Fig. 7.

A c k n o w l e g m s :

T h i s w o r k was i n part supported b y search f r o m the Japanese Ministry of

(No. 57216012).

5000 7000 9000

MAGNETIC FIELD ( G )

Fig.5 Change in line shape of as-induced ~ l on annealing ~ +

( T=-30 O C

,12Na203T120

*85Sio2 glass)

a Grant-in-Aid for Scientific R e - E d u c a t i o n , Science and Culture

-

.c

\

1 . 0 6

ANNEALING TIME( MIN )

Fig. 6 Conversion of

a-

to @-signal

WARM-UP i ~ 2 - 6 0 ' C 1

4

C O O R D . I

6-SI

^GNAL

FIG.7 C O N V E R S I O N O F a - S I G N A L T O 6 - S I G N A L .

References :

1 . Hosono H . , Kawazoe H., Nishii J., and Kanazawa T . , J. Phys. Chem.,

8 6 ( 1 9 8 2 ) 1 6 1 .

2.

-

Hosono H., Kawazoe H., and Kanazawa T., J. Mat. S c i . ,

16

( 1 9 8 1 ) 5 7 .

3 . Hosono H . , Nishii J., Kawazoe H., and Kanazawa T., J. Phys. Chem.,

8 4 ( 1 9 8 0 ) 2 3 1 6 .

4.

=sono H., Kawazoe H , , Nishii J., and Kanazawa T., J. Non-Cryst.

Sol., 44 ( 1 9 3 1 ) 149..

5. Hosono?., Kawazoe H., Nishii J., and Kanazawa T . , 3 . Non-Cryst.

Sol., to be published.

6 . Wells A . F . , "Structural Inorganic Chemistryn Clarendon Press ( 1 5 7 5 ) Chap. 2 6 .

7. Majumdar C.K., Solid State Commun.,

2

( 1 9 7 1 ) 1 0 8 7 .