Phase Evolution and Microstructural Studies in CaZrTi_2O_7-Nd_2Ti_2O_7 System

摘要

A series of compositions with general stoichiometry Ca_(1-x)Zr_(1-x)Nd_(2x)Ti_2O_7 has been prepared by high-temperature solid-state reaction of component oxides and characterized by powder X-ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi_2O_7-Nd_2Ti_2O_7, system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zircono-lite, cubic perovskite, cubic pyrochlore, and monoclinic Nd_2Ti_2O_7 structure types are observed in this system. The 4M-polvtype of zirconolite structure is stabilized by substitution of Nd~(3+) ion. The addition of Nd~(3+) ions form a cubic perovskite structure-type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure-type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca~(2+) and Zr~(4+) are incorporated into the perovskite-type Nd_2Ti_2O_7 structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd~(3+)-rich compositions.