LOW-TEMPERATURE STRUCTURAL PHASE-TRANSITION IN ZRO2-12 MOL-PERCENT 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 spectro scopy and X-ray diffractometry (XRD). When the ZrO2-12 mol% CeO2 was c ooled, the t --> m phase transition occurred at about 120 K; this caus ed significant changes in the infrared reflectance spectra and X-ray d iffractograms. As the phase transition proceeded, ''difference spectra '' obtained by subtracting the infrared spectra before and after the p hase 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 (dete rmined by XRD) and the subtraction coefficient (defined such that the difference spectra reproduced the infrared spectrum of m-ZrO2) were co nsistent with each other; this revealed a marked discontinuity at abou t 120 K. Full width at half maximum of the (111BAR)m and (111)t reflec tions also indicated a similar discontinuity at about 120 K.