X-ray and dielectric studies of irradiated Perovskite type compounds

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X-ray and dielectric studies of irradiated Perovskite type compounds

S.P. Solov’Ev, I.I. Kuzmin, V.V. Zakurkin, V. Ja. Dudarev

To cite this version:

S.P. Solov’Ev, I.I. Kuzmin, V.V. Zakurkin, V. Ja. Dudarev. X-ray and dielectric stud- ies of irradiated Perovskite type compounds. Journal de Physique, 1972, 33 (4), pp.443-445.

�10.1051/jphys:01972003304044300�. �jpa-00207269�

443

X-RAY AND DIELECTRIC STUDIES

OF IRRADIATED PEROVSKITE TYPE COMPOUNDS

S. P. SOLOV’EV, ^{I. I.} KUZMIN, ^V. V. ZAKURKIN and V. Ja. DUDAREV

Karpov Institute of Physical Chemistry, Moscow, ^USSR (Reçu ^{le 16 novembre} 1971)

Résumé.

On obtient _par irradiation gamma de 60Co ou électrons rapides ^{le même} changement réversible de la perméabilité diélectrique ^{dans des} échantillons polycristallins BaTiO3, SrTiO3, PbTiO3, NaNbO3 et PbZrO3. Après irradiation de PbTiO3 dans la pile jusqu’au ^flux intégré ^de

neutrons rapides 03A6 > 1020 cm-2, ^{on a mis en évidence une} transformation structurale vers un

état amorphe qui ^est suivie par la formation d’une phase 03B2-PbO2. ^{En même} temps ^le change-

ment des paramètres réticulaires dans PbTiO3 montre la tendance à la transformation d’état induite _par irradiation qui ^est analogue à celle dans BaTiO3 ^et PbZrO3.

Abstract.

As a result of irradiating polycrystalline samples ^of BaTiO3, SrTiO3, PbTiO3, NaNbO3 and PbZrO3 by ^fast electrons, ^and by gamma-radiation ^of Co60, qualitatively ^identical

reversible changes in the dielectric constant have been revealed. X-ray ^{evidence of the} crystal

structure transformation into an amorphous state, ^followed by the formation of a 03B2-PbO2 phase,

have been found in PbTiO3 ^{as a} result of in-pile irradiation by ^{fast neutron} integrated ^fluxes

03A6 > 1020 cm-2. Lattice parameter measurements in PbTiO3 ^{indicate a} tendency toward the radia- tion induced phase transformation, analogous ^{to that of BaTiO3 and PbZrO3.}

LE JOURNAL DE PHYSIQUE TOME 33, ^AVRIL 1972,

Classification : Physics ^Abstracts

17.29

Experimental data obtained in the last _years have made it possible ^to outline the general features of processes which take place ⁱⁿ perovskite type ^mate- rials under the effect of various irradiation condi- tions [1]. Nevertheless additional information is necessary ^to solve a number of problems concerning

the nature of reversible and irreversible radiation effects in various materials of this type.

This work deals with a study ^{of the} experiments pertaining ^{to two} aspects ^{of the} problem ^mentioned

above.

1. The effect of électron and _gamma irradiation

on the dielectric constant of some ferro-, antiferro-, ^and paraelectric perovskites.

Changes ^{of low field die-}

lectric constant (e) ^for polycrystal SrTi03, BaTi03, PbZr03, NaNb03, PbTi03 ^{which occur} because of gamma and fast electron irradiation are shown in

figures ^{1 a and 1 b} respectively (also ^see [2]). ^Radiation

stability ^of SrTi03 appears ^to be maximum but that of PbTi03-minimum though qualitative changes ^{of a}

are similar for all the compounds ^under study.

Herewith electron _energy (1.14 ^{and 9.0} MeV) ^and

also dose rate (100 ^{and 400} rd/s) changes ^{do not}

affect the nature of the changes ^{of 8.} Crystal ^lattice parameters ^{of all the} irradiated materials remain

unchanged within + 0.001 À.

Radiation induced changes ^{of 8 vanish as a result of} subsequent annealing ^{at 150 °C for about an hour.}

Therefore one may consider these changes ^{to be}

reversible [1], [3], [4] ^and they ^{may be treated as}

radiation induced ageing found earlier on the s

values measured both in high [5] ^{and low electric}

fields [6].

In the course of irradiation the accumulation of rever-

sible defects are accompanied by ^the annealing ^{both of}

FIG. 1.

Changes ^of low field dielectric constant of poly- crystal BaTiO 3, PbTiO 3, PbZrO 3, NaNbO 3, SrTiO3 ^{measured at}

room temperature ^vs integrated ^dose of irradiation : a) by ^fast electrons (E ^{= 1.14} MeV ; ^flux density

^{5 x 1012} cm-2. s-1) ;

b) by gamma-rays of Co6o (dose rate 100-400 r/s).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01972003304044300

444

the radiation and the natural defects in the virgin

material [5]. ^This annealing explains ^the increase of e

in some irradiated samples ^of SrTio3 (Fig. 1 b). ^It

follows from the given ^{data that the conclusion}

(which ^{we have arrived at earlier} [5]), concerning ^the

common physical ^{nature of the} interaction of electron and _gamma radiation (through ^the Compton ^elec- trons) ^with BaTi03, holds well for all the materials which we have studied.

It is noteworthy ^{that the} observed radiation changes

of ^e appear ^to be independent ^{of the} dielectric _pro-

perties ^{of the} compounds (ferro-, antiferro-, paraelec- trics) ^{and must be due} only ^{to the} character of the

packing ^and disordering ^{of the} structural elements AO and B02 ^when one uses a molecular model of

AB03-crystals [3], [4] ⁱⁿ interpreting ^reversible

radiation effects.

2. Crystal ^structure transformations in PbTi03 highly irradiated by ^{fast neutrons.}

^{It has been}

shown [2], [3], [7] ^{that the} irradiation of PbTi03 by ^{fast neutrons with} integrated ^fluxes up ^to T = 8 x 1019 cm-2, gives ^{rise to the Curie} point (T,,

shift to higher temperatures ^{and to the} increase of the tetragonality ^{of the} crystal ^lattice (c/a), ⁱⁿ

contrast with BaTi03 ^and PbZr03, ^{whose values of} cla

decrease with increasing 0 until the radiation induced

phase transition from tetragonal ^to cubic takes place

at 4Y 1019 cm-2.

In the case of PbTi03 ^a continuous increase of cla

is accompanied by the deterioration of the X-ray

diffraction pattern typical ^of perovskite type lattices,

and by the reduction of metallic _{Pb upon} irradiation of Cd-shielded samples (T - 300°C) with fluxes _{up to} 0 ~_ 8 ^x 1019 cm-2 [3], [4]. ^To explain ^{the unusual}

behaviour of PbTi03 ^we have carried out X-ray powder measurements at 0 up ^to 2 ^x 102° cm-2 using the method described in [2], [3]. ^{In contrast}

with our earlier experiments ^the irradiation of the

samples ^{has been} accomplished ^without Cd-shielding

at 40-70 OC.

A brief account of the results obtained is as follows.

With increasing 0 the diffraction pattern ^of PbTi03

deteriorates and at 0 > 102° cm-2 vanishes comple- tely. ^{At the same time a} diffraction pattern ^{of the}

P-PbO2 phase appears. The formation of the P-PbO2 phase ^{also was found in} highly irradiated PbO. The appearance of fl-Pbo2 instead of Pb probably ^is due to different temperature conditions of irradiation of Cd-shielded and unshielded samples.

It is noteworthy ^{that the} annealing ^{of irradiated} samples ^of PbTi03 ^{for 2-3 hours at} 300°C causes a

vanishing ^of the diffraction pattern ^of P-Pb02 ^and

a reappearing ^{of the} fairly ^distinct diffraction pattern of PbTi03 tetragonal phase ^with slightly changed

lattice parameters (Fig. 2). ^A prolonged annealing

at 600°C does not give ^{rise to} additional changes ⁱⁿ

the X-ray diffraction pattern ^of PbTi03.

FIG. 2.

Lattice parameters of PbTi03 ^{vs fast neutron inte-} grated ^{flux before and after} annealing ^{at 300°} during ^{3 hours} (dotted lines). ^The accuracy of measurements Aa = + 0.01 A ;

Ac == :L 0.03 A ^before annealing ^{and Aa}

^Ac = iL 0.003 A after annealing.

The data shown in figure ^{2 seem to state for sure}

that the behaviour of fast neutron irradiated PbTi03

is qualitatively ^{similar to that of} BaTiO. [3], [4], [7]

and PbZr03 [7]. ^{From the} cla tendency ^{to the decrease}

at T > 1020 cm-2 one can expect ^{the radiation} induced phase transition in PbTi03 ^at q, c > 2 ^x 102° cm-2. Corresponding values of q, c

for BaTi03 (N ^{5 x 1018 cm-2} [3], [4], [7]), ^PbZrO3 (N ^{2 x 1019 cm-2} [7]) ^and PbTi03 (> ^{2 x 102°} cm-2)

are in agreement ^{with the} differences of their Curie

points (1200C, ^{230 °C} and 490 °C respectively).

This fact is in favour of the validity ^{of our statement} concerning ^the character of radiation induced phase

transformations in perovskite type compounds [3], [4].

The disappearance ^{of the} PbTi03 X-ray diffraction pattern ^{at 4l} > 102° cm-2 indicates an amorphisation phenomenon ^{known for} materials of different types

(e. ^{g. see} [8]). ^{However this} amorphisation ⁱⁿ PbTi03

is quite different because of the much lower tempe-

ratures ( N 300,DC) ^of annealing ^{of the radiation}

defects. It means that these radiation defects must be due to the above mentioned disordering ^{of AO}

and B02 structural elements and can not be statistical Frenkel point ^defects.

It is reasonable to assume that in contrast with the

case of gamma ^and electron irradiation the disordering

of AO and B02 ^{« molecules » in the course of neutron}

irradiation _goes on up to the total destroying ^{of the}

atomic periodicity arrangement ^{and hence} up ^to the

disappearance ^{of coherent} X-ray scattering. Taking

into account this assumption ^{one can treat all the} changes ^of PbTi03 X-ray diffraction patterns ^{as a} result of irradiation and subsequent annealing. ^{It is}

also possible ^to give ^{a tentative} explanation (see [9])

to the formation of p-PbO2 ⁱⁿ highly ^irradiated PbTi03 ^{and PbO. However further} information is necessary ^to give ^{a detailed account of this} interesting

effect.

445

References

[1] ^SOLOV’EV (S. P.), ^KUZMIN (I. I.), Izv. Akad. Sci. USSR, Ser. Fiz., 1970, 34, ^2604.

[2] ^ZAKURKIN (V. V.), ^SOLOV’EV (S. P.), ^KUZMIN (I. I.),

Izv. Akad. Sci. USSR, ^Ser. Fiz., 1971, 35, 2018.

[3] ^KUZMIN (I. I.), ^SOLOV’EV (S. P.), ^ZAKURKIN (V. V.),

Izv. Akad. Sci. USSR, ^Ser. Fiz., 1969, 33, ^354.

[4] ^SOLOV’EV (S. P.), ^KUZMIN (I. I.), ^ZAKURKIN (V. V.), Ferroelectrics, 1970, 1, ^19.

[5] ^SOLOV’EV (S. P.), ^KUZMIN (I. I.), KHARCHENKO (V. A.),

Izv. Akad. Sci. USSR, ^Ser. Fiz., 1967, 31, ^1757.

[6] STARODUBTSEV (S. V.), ^AZIZOV (S. A.), ^DOMO-

RYAD (I. A.), ^PESHIKOV (E. V.), ^HIZNI-

CHENKO (L. P.), ^« The Effect of Nuclear Radiation

on Materials ». Akad. Sci. USSR, Moscow, 1962, 347.

[7] ^HAUSER (O.), ^SCHENK (M.), Phys. ^Stat. Sol., 1966, 18,

547.

[8] KONOBEEVSKY (S. T.), « The Effect of Irradiation on

Materials » ^« Atomizdat », Moscow, 1967.

[9] ^SOLOV’EV (S. P.), ^DUDAREV (V. Ya), ^ZAKURKIN (V. V.),

KUZMIN (I. I.), Izv. Akad. Sci. USSR, ^Ser. Fiz., 1971, ^{35, 1955.}

ERRATUM

Article : ^« Détermination semi-analytique ^de l’équation d’état des métaux. Application

à la détermination de propriétés élastiques ^et thermodynamiques ^{des métaux sous haute} pression. »

par MIGAULT (A.) Journal de Physique-1971-32 (Mai-Juin) ^437.

A la place ^{de la relation} (7) ^{lire :}

UK = - c ^{+ A exp [- BX113]}

tous les calculs sont corrects.