| Abstract
| - Three new perovskites, CaCu3Ga2Sb2O12, CaCu3Ga2Ta2O12, and CaCu3Ga2Nb2O12, have been synthesized at 12−12.5 GPa and 1100 °C, recovered to ambient conditions, and structurally characterized using X-ray and neutron powder diffraction. These materials represent the first examples where both 3:1 A-site cation order and rock salt B-site cation order have been observed simultaneously.
- Three new perovskites, CaCu3Ga2Sb2O12, CaCu3Ga2Ta2O12, and CaCu3Ga2Nb2O12, havebeen synthesized at 12∼12.5 GPa and 1100 °C using the uniaxial split sphere anvil typepress (USSA-2000) and recovered to ambient conditions, where they have been structurallycharacterized using X-ray and neutron powder diffraction. The large differences in the sizeand bonding preferences of Ca2+ and Cu2+ stabilize a large a+a+a+ octahedral tilting distortionin all three compounds. This distortion creates a 12-coordinate icosahedral site for Ca2+and a 4-coordinate square-planar site for Cu2+. In addition to this A-site cation ordering,CaCu3Ga2Sb2O12 and CaCu3Ga2Ta2O12 also exhibit a rock salt ordering of the octahedralB-site cations. The B-site cation order decreases from 98% in CaCu3Ga2Sb2O12 to 70% inCaCu3Ga2Ta2O12 to effectively no long range order in CaCu3Ga2Nb2O12. These materialsrepresent the first examples in which both A-site cation order and rock salt B-site cationorder have been observed simultaneously. The dielectric constants of CaCu3Ga2Sb2O12 andCaCu3Ga2Ta2O12 were measured to be approximately 12 and 27, respectively, at 100 kHz.Prospects for synthesizing further perovskites exhibiting ordering of both the A- and B-siteions is evaluated using the software program SPuDS.
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