Ti(III) in synthetic pyrope; a single-crystal electron paramagnetic resonance study

Electron paramagnetic resonance measurements were undertaken on a synthetic Ti-bearing pyrope single crystal of approximate composition Mg (sub 3.01(2)) Al (sub 1.93(2)) Ti (sub 0.04(1)) Si (sub 3.00(2)) O (sub 12) in order to further (Geiger et al., 2000) characterize the oxidation state of titanium. The crystal was synthesized hydrothermally at high pressure and temperature and starting with Ti (sub 2) O (sub 3) . The angular dependence of the observed EPR spectrum can uniquely be interpreted as being due to an electron centre with spin 1/2 on a site of 3 point symmetry. It is proposed, based on the composition of the pyrope and its known structure, that the EPR spectrum results from a small concentration of Ti(III) on the octahedral 16a site. Based on previously published optical absorption measurements and microprobe analysis, most of the octahedral Ti should be in the oxidation state (IV).