Low-Temperature Structural Phase Transition in ZrO2–12 mol% CeO2 Studied by Infrared Spectroscopy and X-ray Diffractometry

The low-temperature tetragonal ( t ) to monoclinic ( m ) phase transition in ZrO₂–12 mol% CeO₂ was studied by Fourier-transform infrared spectroscopy and X-ray diffractometry (XRD). When the ZrO₂–12 mol% CeO₂ was cooled, the t → m phase transition occurred at about 120 K; this caused significant changes in the infrared reflectance spectra and X-ray diffractograms. As the phase transition proceeded, "difference spectra" obtained by subtracting the infrared spectra before and after the phase transition revealed two infrared modes at 575 and 740 cm⁻¹ which were assigned to the m phase. The volume fraction of the m phase (determined by XRD) and the subtraction coefficient (defined such that the difference spectra reproduced the infrared spectrum of m -ZrO₂) were consistent with each other; this revealed a marked discontinuity at about 120 K. Full width at half maximum of the ( 1 11) _m and (111) _t reflections also indicated a similar discontinuity at about 120 K.