Phase Stabilization of ZrO_2 Polymorph by Combined Additions of Ca~(2+) and PO_4~(3-) Ions Through an In Situ Synthetic Approach

摘要

This study has been aimed at the phase stabilization of tetragonal Zirconia (t-ZrO_2) by the additions of Ca~(2+) and PO_4~(3-) through an in situ synthetic approach. A wide range of variations have been attempted in which the precursor concentrations of Ca~(2+) and PO_4~(3-) have been maintained constant for every synthesis. The characterization results from XRD, Raman spectra, FT-IR spectra, XRF, and the quantitative analysis have confirmed the t-ZrO_2 stabilization for the selected concentrations ranging from 5% to 20% of Ca~(2+) and PO_4~(3-) in the ZrO_2 system at 900℃. Pure ZrO_2 system without the additions of Ca~(2+) and PO_4~(3-) have yielded the mixture of c-ZrO_2 and m-ZrO_2 at the investigated temperatures ranging between 800℃ and 1000℃ with no identified traces of t-ZrO_2. Thus, the stabilization of t-ZrO_2 has been mainly attributed to the combined influence of Ca~(2+) and PO_4~(3-) presence in the ZrO_2 matrix creating oxygen vacancies that has been confirmed from impedance measurements. Heat treatment beyond 900℃ had resulted in the phase degradation leading to the formation of mixture of phases comprising of major amount of m-ZrO_2 and minor amount of t-ZrO_2.