MÖSSBAUER STUDY OF THE STATE OF IMPURITY ATOMS IN TiO2 - AND BaTiO2 -BASED INSULATING AND SEMICONDUCTIVE CERAMICS

(1)

HAL Id: jpa-00218504

https://hal.archives-ouvertes.fr/jpa-00218504

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

MÖSSBAUER STUDY OF THE STATE OF

IMPURITY ATOMS IN TiO2 - AND BaTiO2 -BASED INSULATING AND SEMICONDUCTIVE CERAMICS

V. Yarmarkin, S. Teslenko, A. Motorny, A. Shustrov

To cite this version:

V. Yarmarkin, S. Teslenko, A. Motorny, A. Shustrov. MÖSSBAUER STUDY OF THE STATE OF IMPURITY ATOMS IN TiO2 - AND BaTiO2 -BASED INSULATING AND SEMI- CONDUCTIVE CERAMICS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-375-C2-377.

�10.1051/jphyscol:19792132�. �jpa-00218504�

(2)

JOURNAL DE PHYSIQUE Colloque C2, supplt%nent au

n o

3, Tome 40, mars 1979, page C2-375

MoSSBAUER

STUDY OF THE STATE

O F

IMPURITY

A T O M S

I N

T i 0

- AND

B a T i O

-BASED

INSULATING

AND

2 2

S E M I C O N D U C T I V E C E R A M I C S

V.K. Yarmarkin, S.P. Teslenko, A.V. Motorny and A.A. Shustrov Ministry of Electronic Indzstry, U.S.S.R.

RQsum6.- L'Qtude de 1'6tat chimique des atomes d1impuret6 de fer, d'antimoine et de terbium (de dysprosium) dans des matQriaux B base de bioxyde de titane de baryum tQmoigne de l'apparition dans ces mat6riaux d'une micro-hQt6rogQnQit6, m@me 1 des niveaux de dopage assez faibles (au-dessous de 1 1 2%

at.). Nous avons trouvQ que les propri6tLs des mat6riaux QtudiQs dQpendent dans une large mesure de l'interaction chimique entre les impuret6s de type donneur et de type accepteur; cette interaction provoque une augmentation mutuelle de la solubilitd de ces impuretQs dans la matrice; cet effet est analogue 1 l'influence mutuelle d'impuretQs "donneurs" et "accepteurs" dans des semiconducteurs clas- siques tels que le silicium et le germanium /9/. Ces rQgularitQs peuvent apparemment Stre Qtendues 1 un groupe assez large de mat6riaux de type oxyde.

Abstract.- The study of the chemical state of iron, antimony and terbium (dysprosium) impurity atoms in materials based on titanium dioxide and barium titanate points to microheterogeneity appearing in these materials already at rather low impurity concentrations (below 1 to 2 at.%). We have found that of great importance ot the properties of the materials studied is chemical interaction between donor and acceptor impurities which results in a correlation increase of their solubilities in the matrix, this effect being similar to the mutual influence of donor and acceptor impurities in classical semi- conductors such as silicon and germanium /9/. The regularities revealed can apparently be extended to a fairly large group of oxide materials.

1 . Introduction.- Among the ceramic oxide materials

for which the question of the mechanism of the effect of impurities, heat treatment and other factors is of great practical importance, barium titanate and solid solutions on its basis should be mentioned. It seems also reasonable to study these problems on simpler materials which can serve for elaborating models. A suitable model can be provided by titanium dioxide which shows many properties and regularities inherent also to other oxides including barium titanate.

Many regularities in the variation of the properties of oxide materials by doping and heat treatment /I-2/ are fairly well explicable within the framework of the classical theory of point defects in solids. The present paper adduces arguments in favour of an essential role of chemical interaction of impurity atoms between themselves as well as with matrix atoms already at rather low doping levels

(see also / 3 / ) .

2. Experimental.- The content of impurities (Fe, Nb, Sb, Tb) was varied from tenths to units of at.%. Ter- bium was introduced as component of thermal-neutron- irradiated gadolinium oxide in which the concentration of 61Tb nuclei was about 0.001 at.%.

The structure and phase composition of the material, the actual content and distribution of the dopant and the chemical state of impurity atoms were

studied by X-ray diffraction, emission and electron microprobe analyses, ESCA and Mzssbauer spectrosco- PY.

Isomer shifts were measured with respect to InSb, sodium nitroprusside and DyF3 for 121sb, "17e and 1 6 1 ~ y , respectively.

3. Results and Discussion.- It has been shown that with a donor impurity content up to 1.2 at.% Sb in

titanium dioxide the Mgssbauer spectra of lZ1sb nuclei do not depend on the dopant concentration the presence of FezOs charge-compensating additive or the conditions of heat treatment of the material. Of special significance to the understanding of the role played by pentavalent impurity ions in conver- ting titanium dioxide into a semiconductive state is the fact that heat treatment of the doped material in air which brings it back to an isulting state in thin layer does not change the valent state of antimony ions.

A similar behaviour is also observed for antimony impurity ions in BaTiOs /5/ which refutes the model suggested in /6/ to explain the concentration dependence of conductivity. For both quasibinary systems, an increase of the impurity content above 1.2 at.% Sb results in a second phase, Ti0.j2SbzOs and BaSbeOs, respectively.

It is seen from the ~zssbauer emission spectra of lslTb nuclei in barium titanate /5/

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792132

(3)

C2-376 JOURNAL DE PHYSIQUE

that with impurity concentrations up to 0.4 at.% Gd, of iron in antimony-doped titanium dioxide. The dysprosium ions forming by the 8-decay of l6?b nu- study of the diffusion of iron in niobium-doped ti- clei stabilize in a trivalent state a further in- tanium dioxide by tracers suggests that it is possi- crease of the impurity concentration results in te- ble to generalize the observed phenomenon.

travalent dysprosium ions and the spectrum of spe-

resulting valency of dysprosium ions /7/; introducing lantanum almost doubles the relative intensity of the peak of tetravalent dysprosium whereas introducing ytterbium ions results in an almost complete disappearance of this peak. A plausible explanation of the above observations could be associated with the fact that terbium ions may enter the barium sublattice where a trivalent state is more prefera- ble for dysprosium ions and the titanium sublattice alike to form D ~ ions. The lastest situation also ~ + may to have as consequence the formation of a second phase in the system.

It has been shown /4/ that unlike antimony, the state of iron ions in titanium dioxide substantially depends on their concentration, the conditions of synthesis and additional heat treatment of specimens and the presence of a donor impurity in the material. Because of a complexity of some spectra of the ceramics the investigation was continued.

A further evidence in favour of the interpretation given in 141 is the Mgssbauer spectrum for a speci- men of the formulation BaTi03 + 2 at.% Fe below the N6el temperature of the Fe2TiOs compound, 50 K 181.

This spectrum is made up of a doublet ascribed to Fe3+ ions dissolved in TiOz and a magnetically split spectrum identical to the spectrum of Fe2TiOs at the above temperature. One can also see for comparison the Mgssbauer spectra of iron introduced into a single crystals by means of thermal diffusion (Fig.1).

Also note that iron diffusion is faster along the C axis of the rutile-like structure (the corresponding diffusivity is greater at least by an order of ma- gnitude at 1 10oOc), which speaks in favour of the interstitial diffusion mechanism.

The study of the quasiternary Ti02-Sb20s-Fe03 system 141 has revealed an essential role of chemical interaction of antimony and iron atoms resulting in complexing and in an increase of the solubility cimens containing 2 at.% of the impurity is identical

1

to the emission spectrum of the BaT03 + 2 at.% Gd

-4d ... 31

ceramic which has the same perovskite structure as

5 3 1 barium titanate. Introducing other lantanoids joint- ^U_Z

rn L

m.

ly with the irradiated gadolinium oxide into BaTiO3

...

*

..

Q

(approximately equal quantities of lantanum or u L f@.".,

ytterbium oxides were added so that the total impu-

Fig. I : ~gssbauer absorption ( I ) and internal-conversion electron (2) spectra of " ~ e nuclei of iron ions in Ti02 single crystals (specimens ground from the side of the diffusion source at 30 pm dept5) : (a) the C axis parallel to incident gamma quanta, (b) the C axis perpendicular.

The above-mentioned interaction which results in the

"binding" of pentavalent ions by trivalent ones is equivalent to a decrease of the effective concentration of donor impurity ions and accordingly reduces their effects on the properties of titanium dioxide (specifically the conductivity and the grain size of the ceramic).

To test the suggestion of similar interactions upon doping other oxide materials including those on rity content was 1 at.%) substantially affects the -1 ⁰

' -

² ^-i v e t o c ~ t y ( m m / r ) ⁰

-

²

I#.::.&::% .. .. .._ > .,. . .

..

.>p,;::<:::>:

.

.?, ::..,;t" _:....a\ ...,

".... ....

. ,. - . .

..

^.-

.;:.

:

. :<.

2a

.

.. ...

²

..

.. .:

..'

..

. . . .:.

y,-.

. -

. ..:.--:

^A

.'

^.^'

- .. - .

^.^*^...::.-.-.. ^.

..

....

:':

the basis of barium titanate, a Mhsbauer study was performed on 5 7 ~ e nuclei in pure and niobium-doped barium titanate.

When earlier studying polycrystalline specimens of the quasibinary BaTiO3-Fez03 system /5/,

iron ions were found to be dissolved in both trivalent and tetravalent state, the proportion of either valent state depending on the concentration and synthesis conditions. Of great importance are also the interactions BaO-Fen03 and TiOz-FeOs resulting in barium ferrites and iron titanates. Similar results relating to forming second phases have been obtained in the study of the chemical nature of the the diffusion source on the surface of BaTiO3 single crystals (the initial chemical form of the source was Fe203) by the Mgssbauer spectroscopy on internal- conversion electrons.

Addition of niobium oxide to the quasibinary BaTi03-Fez03 system inhibits the chemical reactions which result in barium ferrites and iron titanates

(Fig. 2). This confirms the suggestion of the mutual effect of impurities with different valency on their solubility in Ti02 and BaTi03 /4/.

.... .. - ^..

':7..:.?{:.,....

.?..,, . ... .'

^..^":^.:

:. . .

.. ^.;p ..-

-. ^'

.-.. . . ^.. ^. ^.::;.

^.^"

.

7

,... ..

..:* ^C. ¹_{. _}^b

I

..

+ _...

_.^{. I}^{- 5}

. .. . -

^I.

..

^I ^2b

I _{. ..}_,..-

- . .

..

-..:

_.

'

_*::

I<.:

.,.. .:.: .

.=:.

a*.:..

& 2 -... .

..:.--

^:.,...-c

(4)

References

/ I / Kofstad, P., "Nonstoichiometry, Diffusion and

Electrical Conductivity in Binary Metal Oxides", (Wiley/Interscience, New York) 1972.

,

^.:a,: /2/ Sheftel, I.T., "Thermistors" (Nauka, Moscow) 1974.

tuu~u*.,.,",~,

.'

;s-+.--r.--r. .--r:-.;*--.::rx*--

..

_.. . .

. .

^: /3/ Yarmarkin, V.K., Ivanov; Kostikov, Yu.P., Martynov, V.B. and Motorny, A.V., I.K., Kvantov, M.A.,

.

ibid., p. 206.

-

",

4

. .

/4/ Yarmarkin, V.K., Teslenko, S.P. and Knyasev, A.I.,

; . . .

... .

^.. ^. ^.^.

)

Phys. Status Solidi (a)

5

(1978) 63.

- 5 10 1 5 1 Yarmarkin, V.K., Shustrov, B.A. and Motorny, A.V.

v e f o c A y (mn/sj

-

Proc. Int. Conf. Mossbauer Spectroscopy, 25-30

Fie. 2

-

: ~Essbauer absor~tion s ~ e c t r a of 5 7 ~ e nuclei Auaust 1975. Cracow. Poland. vol.

^.,

I. ^{. .}D. 325.

(T = 293 K) in ceramics : (1) BaTi03 + 4 at.% Fe and

(2) BaTiO, + 4 at.% Fe + 0.5 at.% Nb. /6/ Schmelz, H., Phys. Status Solidi (b)

21

(1969) 121;

35

(1969) 219.

/7/ Motorny, A.V., 2nd Nat. Conf. Chem. Sol., 11-13 May 1978, Sverdlovsk, USSR, Abstracts, Part 2, p. 37.

/ 8 / Muranaka, S., Shinjo, T., Bando, Y. and Takada,

T., J. Phys. Soc. Japan.

30

(1971) 890.