Glass-Ceramics In The Systems La-Pb-Mn-B-O and La-Pb-Mn-Te-O
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E. GATTEF, A. STANEVA AND Y. DIMITRIEV Higher Institute of Chemical Technology, Sofia-1756, Bulgaria
ABSTRACT Compositions from the systems Pb-Mn-B-O and Pb-Mn-Te-O are used to synthesize glass-ceramics obtained by solid state reactions and from supercooled melts. By casting on a metal plate or by quenching with the aid of twin rollers the melts are cooling. The glasscrystalline materials are obtained after heating glasses from the combination of PbO-MnOB20 3 and PbO-MnO-TeO 2 with the addition of La 20 3 from 10 to 50 wt.% and the formation of the crystalline phases is determined.
INTRODUCTION Manganese perovskite phases La_ Ax MnO 3 (A = Ca, Sr, Ba, Pb) are known as ferromagnetics which possess higher Curie temperature as a result of the positive double exchange interaction between Mn 3÷ and Mn" ions [1, 2, 3, 4]. At high temperatures above 14000 C with the appropriate atmosphere or additives it is possible to vary defects of the sublatticies and even to obtain pure phases in which only Mn 3 ÷exists [5]. More completely investigated are the solid state solutions La, Sr.MnO 3 [6, 7, 8, 9, 10]. A perovskite phase in the system LaPb-Mn-O is also well known [11, 12, 13, 14, 15, 161. The investigation of the phase formation, properties and the application of the manganese perovskites is in progress during last years connected with various applications as catalysts [17, 18, 19], electrodes [20, 21, 22, 23, 24, 25], semiconductor ceramics [26, 27, 28], amorphous ferromagnetics [29, 30] and as layered superconductor devices [31, 32]. An appropriate method to obtain manganite perovskites is the sol-gel process which gives the possibility to synthesize materials at low temperature [33, 34, 35]. Another method to control the synthesis and the properties is the use of the glass technology. In our previous works [15, 161 we reported the formation of glass-ceramics containing perovskite ferromagnetic phases after thermal treatment of glasses in the system La-Pb-Mn-B-Te-O. The object of the present study are compositions from the systems Pb-Mn-B-O and PbMn-Te-O with the addition of La 20 3. Thus this work appears as a further development in the same direction. The purpose is to synthesize new glass-ceramics obtained by solid state reactions and from supercooled melts and to determine phase formation during the heat treatment. 739 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
EXPERIMENTAL The synthesis of the crystalline phases is made in air by solid state reaction of pressed powder batches (particle size 1-5 gim and pressing pressure 2 t-cm-2 , method A). The other technique is obtaining of glasses by twin rollers , grindin g with or without additives, pressing and sintering at appropriate temperature (method B). The melting was performed using alumina or platinum crucibles at temperatures up to 14000C, 20 mn. The phase relations *La 1 -x Pbx~Mn 03 were determined by X-ray (CuK.) diffraction -Pb5 Mfl6O
experiments.
-PbSMn 6O1
RESULTS AND DISCUSSION The investigation performed in the present work
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