Crystal structure, short-range oxygen defects, and water adsorption in La- and Nd-modified ZrO(sub 2)

摘要

Doping Rare-earth (RE) elements to ZrO(sub 2) helps stabilize the cubic and tetragonal phases and improves resistance to thermal shock and sintering at high temperatures. Since a RE ion has a lower valency (3(sup +)) than Zr ion (4(sup +)), oxygen vacancies are formed to preserve electroneutrality. We have studied the crystal structure of La(sub 0.1)Zr(sub 0.9)O(sub 1.95) and Nd(sub 0.1)Zr(sub 0.9)O(sub 1.95) by neutron diffraction and examined the associated oxygen defects by a Fourier transform of the filtered residual diffuse scattering. The hydration process was investigated by inelastic neutron-scattering measurements of the hydrogen vibrational density of states of the surface hydroxyl groups and physisorbed water on these fine powders. We compare the O-H stretch vibrations for samples from with only surface hydroxyl groups to multilayer coverage of water molecules. The decreasing energies and increasing widths of the O-H stretch bands with increasing H(sub 2)O coverage indicate the influence of hydrogen bonding on the motion of water molecules. Similar elastic and inelastic experiments were also performed on a high surface-area pure ZrO(sub 2) powder.