Synthesis and symmetry transformation in the perovskite compounds PbHfO3 and CdHfO3

From high temperature X-ray diffraction experiments the perovskite compounds PbHfO₃ and CdHfO₃ have been shown to undergo a series of structural phase transformations. At 298°K PbHfO₃ is orthorhombic with cell dimensions $\text{a}\text{= 5.8572(5)}\text{A}\text{?}$, $\text{b}\text{= 11.689(1)}\text{A}\text{?}$, $\text{c}\text{= 4.0971(4)}\text{A}\text{?}$ and most probable space group Pnam. At 450°K it is rhombohedral with hexagonal cell dimensions $\text{a}\text{= 5.854(1)}\text{A}\text{?}$ and $\text{c}\text{= 7.145(2)}\text{A}\text{?}$ and at 520°K PbHfO₃ is cubic perovskite with $\text{a}\text{= 4.1354(4)}\text{A}\text{?}$. CdHfO₃ is also orthorhombic at 298°K with cell dimensions $\text{a}\text{= 5.5014(8)}\text{A}\text{?}$, $\text{b}\text{= 5.6607(8)}\text{A}\text{?}$, $\text{c}\text{= 7.969(1)}\text{A}\text{?}$, and space group Pbnm. At 1075°K CdHfO₃ is rhombohedral with hexagonal cell dimensions $\text{a}\text{= 5.747(4)}\text{A}\text{?}$ and $\text{c}\text{= 13.49(1)}\text{A}\text{?}$