PRESSURE-INDUCED STRUCTURAL-CHANGES IN ND2-XCEXCUO4 (X=0 AND 0.165)

The crystal structures of Nd2CuO4 and superconducting Nd1.835Ce0.165Cu O4 under hydrostatic pressure up to 0.6 GPa have been investigated by time-of-flight neutron powder diffraction with a He gas pressure cell. The a and c parameters and the volumes of the tetragonal unit cells d ecreased linearly with increasing pressure. The bulk moduli, K, are 13 4 GPa for Nd2CuO4 and 140 GPa for the Ce-doped sample. These K values lie between those of La1.85Sr0.15CuO4 and La1.82Ca1.18Cu2O6. The compr essibilities along the c axes were about 1.5 times as large as those a long the a axes. The linear compressibilities along the a and c axes a nd the bulk moduli were compared with those calculated on the basis of a simple compression model proposed by Cornelius et al. The negligibl e effect of pressure on the T(c) of Nd2-xCexCuO4 is discussed in conne ction with the crystal data obtained in this study.