Influence of inversion level on the optical absorption spectra of Ti‐doped transparent MgGa2O4 ceramics. Issue 9 (9th May 2022)

• Record Type: Journal Article
• Authors: Zhang, Guangran; Wu, Yiquan; Shames, Alexander I.; Goldstein, Adrian
• Is Part Of: Journal of the American Ceramic Society. Volume 105:Issue 9(2022)
• Page Start: 5944
• Page End: 5955
• Publication Date: 2022-05-09
• Subjects: electron paramagnetic resonance -- optical materials/properties -- spinels -- transparent ceramics; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.18518
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: Ti‐doped (0.08, 0.30, and 1.00 atomic% [at.%]) transparent MgGa2 O4 ceramics (possessing a high inversion level; i up to 0.8) were fabricated by pulsed electric current sintering, at 950°C, under vacuum for 30–90 min. Optical transmission, emission, and electron paramagnetic resonance spectra were recorded. The maximal transmission level was ∼70% (820 nm), for a thickness of ∼1 mm, which, while not very high, permitted the observation of the optical absorption bands location and profile. Interpretation of the fluorescence spectra suggests that some Ti 4+ cations (mostly hexacoordinated) were accommodated by the host despite the scarcity of oxygen in the atmosphere during the sintering process. The Ti 3+ cations substitute native ions located in tetrahedral sites, distorting the original Td symmetry toward a D2d symmetry. Comparing the Ti‐doped MgGa2 O4 (high inversion) and MgAl2 O4 (low inversion) spinels, spectral characteristics revealed that a significant increase in the inversion level drives Ti 3+ cations from octahedral toward tetrahedral sites. This is reflected in the optical absorption spectra by the disappearance of the band at ∼20 000 cm −1 (detectable in MgAl2 O4 ) in MgGa2 O4 ; the two d–d bands, of MgA2 O4, in MgGa2 O4 are reduced to a single one, located at 11 800 cm −1 . These results, for MgGa2 O4, strongly support a similar assignment—of the strong band at 12 800 cm −1, in Ti‐doped MgAl2 O4 —to a tetracoordinated Ti 3+ . Thus, while in MgAl2 O4, Ti 3+ appears in both octahedral and tetrahedral coordination and in MgGa2 O4 only the latter state is stable. In both spinels, Ti dopant speciates into Ti 3+ and Ti 4+ cations.