Crystalline Ta2O5 has very rich defect energy levels as compared to the previously known ones. Thermal treatment of Ta2O5 in a reducing atmosphere increases the photoluminescence (PL) intensity of the deep energy levels in the band gap as compared to the shallow ones. Nitrogen doping creates no new defect energy levels, but rather shifts the maximum PL intensity position of the deep energy levels to even deeper states. The doped nitrogen is interpreted to fill the oxygen vacancy at “in-plane” lattice sites when it is doped to TaO6 octahedron.

In this study, the effect of MgF2 additive on the mechanical properties of hydroxyapatite (HAp)/zirconia composites was investigated. As a fluoride additive, MgF2 was added to HAp/zirconia composites for the suppression of phase decomposition from HAp to tricalcium phosphate (TCP). Due to the dissolution of MgF2 at the phase decomposition temperature of HAp, the phase decomposition of non-stoichiometric HAp was suppressed. When MgF2 (5, 10 vol%) was added to HAp/zirconia composites, the decomposition of HAp was completely suppressed below 1400oC due to the ion substitution F- of for OH- in the HAp crystal structure. The flexural strength and Vickers hardness of composites was revealed more higher values compared with the MgF2-free composites.

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Calcium-hexaluminate phase(CA6) phase is known to be effective for the crack shielding due to the spinel block crystal structure. In this study, we focused to control the CA6 morphology for the good damage tolerance behavior in alumina and zirconia/calcium-hexaluminate(CA6) composites. calcium-hexaluminate(CA6) composites were prepared from zirconia, alumina and calcium carbornate powders. Calcium-hexaluminate(CA6) phase was obtained by the solid reaction through the formation of intermediate phase(CA2). CA6 phase showed column type abnormal grain grown behavior composed of small blocks. Due to the typical microstructure of CA6, alumina and zirconia/calcium-hexaluminate composites provide well controlled crack propagation behavior.