Infrared-reflectivity study of ZrO2-HfO2 solid solutions.

Abstract

Infrared-reflectance spectra of the solid solutions ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$ (0\ensuremath{\le}x\ensuremath{\le}1) have been measured at room temperature in the frequency region 50--4000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ by Fourier-transform infrared spectroscopy in order to study the composition effect on the vibrational properties of ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$. At most, twelve infrared-active modes of 5${\mathit{A}}_{\mathit{u}}$ and 7${\mathit{B}}_{\mathit{u}}$ symmetry were identified in the reflectance spectra of ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$. The spectra of ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$ varied systematically with x, with changes in the frequency, linewidth, and intensity of these modes. Particularly, the ${\mathit{B}}_{\mathit{u}}$ modes at 585 and 606 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{ZrO}}_{2}$ considerably stiffened in a nonlinear way, indicating a pronounced stiffening around x=0.8 as x increases. It was found that the lattice parameters a,b, and c of ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$ decrease linearly with x whereas \ensuremath{\beta} initially increases up to x=0.6 and then decreases towards that of the end member ${\mathrm{HfO}}_{2}$. Hence, it was concluded that the stiffening of all other modes except a ${\mathit{B}}_{\mathit{u}}$ mode is associated with the bond reinforcement evidenced by the reduced cell volume of ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Hf}}_{\mathit{x}}$${\mathrm{O}}_{2}$ as the ${\mathrm{Hf}}^{4+}$ ions of smaller radius are substituted for the ${\mathrm{Zr}}^{4+}$ ions. It was also concluded that the anomalous feature around x=0.8 in the frequency, linewidth, and intensity of the modes as a function of x can be reconciled with two-mode behavior, which has been characterized by discontinuities at either x=0.6 or 0.3 in the x dependence of seven Raman mode frequencies for ${\mathrm{Zr}}_{\mathit{x}}$${\mathrm{Hf}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{O}}_{2}$ [C. Carlone, Phys. Rev. B 45, 2079 (1992)].