Novel transparent MgGa2O4 and Ni2+-doped MgGa2O4 ceramics

Abstract

In this study we fabricated, for the first time, magnesium gallate (MgGa2O4, a partially inverted spinel) transparent ceramics, both undoped and doped with 1 at% Ni. The specimens were derived from in-house prepared powder, with a crystallite size of ∼10 nm (by wet chemistry) and densified by pulsed electric current sintering (PECS; peak temperature 950 °C for 90 min). Densification levels of 99.84% and 99.52% of theoretical density were attained for doped and undoped materials, respectively. Doping with Ni was seen to marginally improve the densification level. Quite transparent specimens were produced: the best showing transmission of ∼89% of the theoretical level (thickness t = 0.85 mm). The absorption spectra revealed that the dopant was accumulated as Ni2+ in the octahedral sites of the lattice, as occurs in single-crystal specimens. After excitation at 980 nm, the doped disks exhibited a wide fluorescence band centered at 1264 nm.

Influence of inversion level on the optical absorption spectra of Ti‐doped transparent MgGa2O4 ceramics

“…The optical spectra (Figures 2–4) show strong absorption in the UV range. The relatively medium width bandgap (∼4.7 eV 12 ) of MGO corresponds to a cutoff edge, of the fundamental (i.e., band to band transitions owed) absorption, placed at ∼280 nm. It is important to observe that the recorded UV low‐energy edge line of Ti:MGO has a curved shape, markedly red‐shifted compared to the fundamental absorption cutoff, at 280 nm, absorption decreases significantly only over 370 nm.…”

“…The accommodation in octahedral sites, observed here for Ti 3+ , is not meant for all 3d cations introduced in the MGO lattice. For instance, Ni 2+ enters octahedral sites in MGO 12 . It is likely that this difference in behavior stems from the more significant differences between the CFSEs corresponding to octahedral and tetrahedral coordination in the case of Ni 2+ (diff.…”

“…Fabrication of transparent MGO ceramics was described in detail elsewhere 12 ; only the main points are recapitulated here. The raw materials used to generate the host were Mg(NO 3 ) 2 ·6H 2 O (99.999%; Sigma‐Aldrich, USA) and Ga(NO 3 ) 3 ·H 2 O (99.9%, Alfa Aesar, USA).…”

“…Transparent MGO ceramics are chosen as subject for experiment due to simple and convenient fabrication processing when compared to single crystals of the same composition. It was obtained based on a procedure we recently developed to produce transparent MgGa 2 O 4 (T‐MGO) specimens 12 . The measured data of T‐MGO was then compared with MAO, whose related information are available from previous studies (both our own and literature) 4,13–17 .…”

“…It was obtained based on a procedure we recently developed to produce transparent MgGa 2 O 4 (T-MGO) specimens. 12 The measured data of T-MGO was then compared with MAO, whose related information are available from previous studies (both our own and literature). 4,[13][14][15][16][17] Hosts selection and their processing procedure were determined with care, for this study, to minimize potential influence on the spectra due to factors other than the i values.…”