MATS- Y 69-0545 .

Reprinted from the Journal of The American Ceramic Society. Vol. 52. No.9 September 21, 1969. Copyright 1969 by The American Ceramic Society

High-Pressure Synthesis of Perovskite-Type Pb(Znl/3Nb2/3)O 3 YOSHIHIRO MATSUO, HIROMU SASAKI, SHIGERU HAYAKAWA, FUMIKAZU KANAMARU, and

MITSUE KOIZUMI

SEVERAL perovskite-type compounds All (Bll,/,NbV",)0, have

been reported'-- (Table I); Pb(Zn,/3Nb.,,)O. has been syn-thesized only in single crystal form using a lead oxide flux.'" The present authors attempted to prepare a perovskite-type Pb(Zn'~M)O. by the usual ceramic techniques. The product was a pyrochlore-type Pb.Nb,O;:

3PbO + ZnO + Nb.0. -7 PbaNb.O. + PbO + ZnO The coordination number of Pb with oxygen is 8 in Pb,Nb,O,

and 4 in tetragonal PbO, and that of Zn is 4 in ZnO. Under high pressure, ZnO transforms from the wurtzite-type (4-coordination) to NaCI-type (6-coordination)" structure, and PbO, transforms from the rutile-type (6-coordination) to the fluorite-type (8-coordination) ' structure.

In the present study, a high-pressure technique was adopted to obtain perovskite-type Pb(Zn'/'Nb.,, ) 0,. Chemically pure PbO, ZnO, and Nb,O. were mixed in the molar ratio 3: 1: 1, respectively. The mixture was placed in a platinum tube 3 mm in diameter and 10 mm long which was inserted into a pyrophyllite capsule with a cylindrical graphite heater. The samples were treated at pressures of 15 to 25 kbars and tem-peratures of 600° to llOO°C using a piston-cylinder type of high-pressure vessel. After 10 min to 2 h under these condi-tions, the specimens were air-quenched and decompressed.

Received December 2, 1968; revised copy received June 26, 1969.

Yoshihiro Matsuo, Hiromu Sasaki, and Shigeru Hayakawa are with the Wireless Research Laboratory, Matsushita Elec-tric Industrial Company, Ltd., Osaka, Japan. Fumikazu Kana-maru and Mitsue Koizumi are with the Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.

1 V. A. Bokov and 1. E. Myl'nikova, "Ferroelectric Proper-ties of Monocrystals of New Perovskite Compounds," Soviet Phys.-Solid State (English Trans!.), 2 [11] 2428-32 (1961).

, Hiromu Sasaki and Shigeru Hayakawa, " Growth of Single Crystal of Pb(Zn"aNb",)O. and Its Properties"; preprint for the llth Annual Meeting of Symposium on Synthetic Minerals, Sendai, Japan, October 1966.

, G. A. Smolenskii and A. 1. Agronovskaya, "Dielectric Polarization of a Number of Complex Compounds," Soviet Phys.-Solid State (English Transl.), 1 [10] 1429-37 (1960).

4 Francis Galasso, Lewis Katz, and Roland Ward, "Substitu-tion in the Octahedrally Coordinated Cation Positions in Com-pounds of the Perovskite Type," J. Am. Chem. Soc., 81 [2] 820-23 (1959).

• Francis Galasso, J. R. Barrante, and Lewis Katz, "Alkaline Earth-Tantalum-Oxygen Phases Including the Crystal Struc-ture of an Ordered Perovskite Compound, Ba"SrTa,O.," ibid., 83 [7] 2830-32 (1961).

o G. Blasse, "New Compounds with Perovskite-Like Struc-tures," J. Inorg. Nucl. Chem., 27 [5] 993-1003 (1965).

' V. M. Goldschmidt, "Geochemical Distribution Laws of the Elements: VIII," Skrifter Norske Videnskaps-Akad. Oslo, I: Mat. Naturv. KI., 1926, No.8, 7-156 (1927).

Table I. Perovskite-Type Compounds with the Formula An (B'\/3Nb v 2/3 ) 0 3

Lattice Curie Synthesis by Tolerance Coordination No. Coordination No. constant point usual ss factor of A in of BIT in

Compound (A) (OC) reaction (Ref. 7) compound AO compound BUO

Ba (ZnJJ$Nb.,,) 0. 4.10 Possible 0.93 6 4 Sr(Zn".Nbw)0. 4.00 Possible .86 6 4 Pb (Zn"aNb./S) 0. 4.06 140 Uncertain .86 4 or 3 4 Pb(Mg,,.Nb../O)0, 4.04 - 12 Possible .88 4 or 3 6 Pb (Ni".,N9",) 0 , 4.02. - 70 Possible .88 4 or 3 6 Pb (Co",Nb.,,) 0, 4.04 -120 Possible .87 4 or 3 3

September 1969 Journal of The American Ceramic Society-Discussions and Notes 517

30

• 'll +Liq.(PbO) •

~ ~ -_1---0 20 0 I .1:2 ~ - - -

.>0:

'" I Q) 0 I ~ f :::J , 0 0 II> II> +-~ 0 : PbzNbz0 7ss t ZnO ,

I c: PbzNbz0 7ss + Zno a. N 10

.... ~ +PbOss

I 'tUq. (PbO)

~ I

I

I

: Liquid

0 500 700 900 1100 1300

Temperature (OC)

Fig. 1. poT conditions for formation of perovskite.type Ph(Zn".Nb./.)O. Crom mixture with composition 3PhO· ZnO·m,O. : 0 no product, • perovskite phase, 0 pyro·

chlore phase, and f::,. tungsten bronze phase.

The powders obtained were examined by X·ray powder diffrac-tion and electron microscopy.

Figure 1 indicates the phases appearing in each run. The peroYskite-type compound was formed at 25 kbars and 800° to lOOOoe. After reaction at 900 0 e and 25 kbars for 1 h, the main product was peroYskite Pb (Zn,,,Nb,/I ) O. with a minor product of pyrochlore Pb:Nb,O" as shown in Fig. 2(A) . The X-ray diffraction pattern of the main product is quite similar to that of the Pb(Zn,,,N!>,/3 )O. crystals obtained by the PbO flux method. The Pb(ZIh/aNb,/. )O. crystal is considered to be slightly distorted from a cubic lattice, because the higher-angle diffraction lines are slightly split. The microstructure of the compacts of Pb(ZnJ/,Nb,/3 )O, sintered at 25 kbars and 900 0 e for 1 h showed that the grain size was less than 1 /Lm .

The stability of the high-pressure product was checked by X-ray examination of a specimen prepared one month pre-viously. No phase change was observed. The single phase Pb(Zn" ,Nb,/3 ) 0 " however, decomposed into Pb.Nb,O" PbO,

Fig. 2. X-ray powder diffraction patterns for perovskite· type Ph(Znl>.Nh'/3)O, (CuKa radiation). (A) Powder com· pacts synthesized at 25 khars and 900°C for 1 h and (B)

single crystals grown from PhO flux.

and ZnO when heated above 7000 e under atmospheric pres-sure. These results indicate that the perovskite-type com-pounds form only under high pressure. The calculated X-ray densities of Pb.Nb,O, and Pb(ZfiJ/.Nb,/. )'O, are 7.9 and 8.4 g/ cm' , respectively. From this density relation, it is reason-able that Pb(ZfiJ/,Nb,/,)0, is more stable than Pb,Nb,O, at high pressure.

Acknowledgment The . auth~rs are indebted ~o R. Kiriyama for suggestions

and dIscussIons from the. vIewpoint of crystal chemistry. Thanks are also due to T. Miyazawa and J. Maid for assistance during some of the experiments.

8 e. H. Bates, W. B. White, and Rustum Roy, "New High-Pressure Polymorph of Zinc Oxide" Science 137 [3534] 993 (1962) . "

• Y. Syono and S. Akimoto, "High Pressure Synthesis of Fluorite-Type PbO,," Mater. Res. Bull., 3 (2] 153-58 (1968) .

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