INFRARED AND RAMAN-SPECTROSCOPIC STUDIES OF ZRO2 POLYMORPHS DOPED WITH Y2O3 OR CEO2

Infrared and Raman spectroscopic studies of ZrO2 doped with Y2O3 (1, 2 , 3, and 8 mole%) and 12 mole% CeO2 have been done with a conventional X-ray diffraction (XRD) technique. Infrared and Raman spectra of thes e doped ZrO2 polymorphs were well characterized by their unique spectr al features or optical phonons. Low-temperature infrared spectroscopy also revealed that the 580 and 725 cm-1 modes suddenly evolve at about 123 K when the tetragonal (t)-monoclinic (m) phase transition is indu ced in ZrO2-12 mole% CeO2(Z12C); the analysis based on the oscillator strength of the B(u) mode at 580 cm-1 revealed that the t-m phase tran sition occurs discontinuously with a very narrow transition width of a pproximately 2 K, whereas the oscillator strength of the E(u) mode ass ociated with the t-phase decreased toward the phase transition. It was concluded that the nonoccurrence of the t-m phase transition in tetra gonal ZrO2-3 mole% Y2O3(Z3Y) originates in its being less tetragonal ( c/a = 1.012) than Z12C (c/a = 1.018), in the context of the dependence of the transformability on the tetragonality, as proposed by Kim. The downshift in frequency of the Raman modes for Z12C provided more evid ence of a larger axial ratio for Z12C than for Z3Y through an expansio n in the a-axis and the c-axis, as confirmed by XRD. It is stressed th at traces of another existent phase (not predominant) at the surface a nd/or in the bulk can be substantiated by using infrared and Raman spe ctroscopic techniques at the same time as XRD. (C) 1994 Academic Press , Inc.