Phase Transformation and Thermal Expansion of Zirconium and Hafnium Titanates and Their Solid Solutions

Abstract

Phase transformations and thermal expansions were studied for compounds having the α‐PbO 2 type of structure in the ZrO 2 ‐HfO 2 ‐Ti O2 ‐SnO 2 system. Continuous phase transformation of ZrTiO 4 accompanied by a marked shrinkage of the b parameter was confirmed. All the compounds including HfTiO 4 existed as dimorphs, although the difference in the b parameters between the high‐ and low‐temperature forms decreased with the content of Hf and Sn in the Zr 1‐x Hf x TiO 4 system and the Zr x Ti y Sn z O 4 ( x + y + z = 2) system, respectively. The striking contrast in thermal expansions between ZrTiO 4 and HfTiO 4 was confirmed for furnace‐cooled specimens at a rate of 10°C/min. The high‐temperature ZrTiO 4 quenched from 1500°C exhibited thermal expansion significantly smaller than that of the furnace‐cooled ZrTiO 4 . The low‐temperature ZrTiO 4 heated at 1000°C for 720 h exhibited thermal expansion larger than that of the furnace‐cooled ZrTiO 4 . The thermal expansion of furnace‐cooled Zr x Ti y Sn z O 4 ( x + y + z = 2) decreased with the Sn content, and that of ZrTi 0.4 Sn 0.6 O 4 was found to be almost identical with that of HfTiO 4 . A number of anomalies exhibited by these mixed oxides are noticed. And a hypothesis based on the interaction of orbitals by using d electrons of highly charged cations has been proposed to explain the anomalies.