常压烧结和高压合成Nd2-xCexCuO4的结构特征与导电性质

 本文在常压高温和高压高温条件下合成出了Nd_2-xCe_xCuO₄（x=0~0.20）系列样品，对比研究了两种不同条件下合成产物的结构特征与室温至液氮温区的导电性质。测试分析结果表明，高温高压（1.7 GPa，800 ℃，10 min）合成的样品与常压高温（1 000 ℃，10 h）烧结的样品具有相同的四方结构，但晶格常数随掺杂量变化有所不同，高压合成产物的c轴随掺杂量基本不变，而常压烧结样品c轴随掺杂量增加呈下降趋势。两种条件合成的样品在液氮温区均呈现出不同程度的半导体特征，经过一次高温淬火后处理后，高压样品的导电性质明显优于常压样品。实验结果表明，高压可以降低固相反应的合成温度，缩短反应时间，特别是高压的还原作用有利于产物导电性质的改善。

STRUCTURAL CHARACTERS AND THE CONDUCTIVITY OF Nd_(2-x)Ce_xCuO_4 SAMPLES PREPARED UNDER ATMOSPHERE AND HIGH PRESSURE

Samples of Nd_2-xCe_xCuO₄ have been synthesized by using atmosphere pressure-high temperature (AT) and high pressure-high temperature (HP) methods. The structural characters and electrical conductivity of the samples prepared by the two different methods have been studied. The sample synthesized by HP (1.7 GPa, 800 ℃, 10 min) has a tetragonal structure (T' phase), similar to that of the samples sintered by AP (1 000 ℃, 10 h), but their crystal parameter, c, varies in a different manner as the Ce⁴⁺ doping content, x, changes. The parameter c for HP products remains basically constant as the doping content x increases, whereas the parameter c for the AP products decreases obviously as x increases. Both samples prepared by AP and HP methods exhibit semiconducting properties in varying degrees under liquid nitrogen temperatures. The electrical conductivity of the HP samples, quenched at high temperature, is superior to that of AP samples. Experiments show that high pressure is beneficial to reduce the synthesis temperature, to shorten the reactive time of solid state reaction and, particularly, to improve the electrical conductivity of the samples due to the reduction role of high pressure.