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

Abstract

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