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.
Highlights
Magnesium gallate (MgGa2O4) is a stiff, refractory, double oxide, with an intermediate band gap value (~4.9 eV) that makes it possible to produce both insulator and conductive variants, as well as being resistant to decomposition until close to its melting point [1]
Because of the relevance for transition metal (TM) cation spectroscopy of the material, we investigated the spectral behavior of the Ni-doped transparent magnesium gallate ceramics
The two Powder Diffraction File (PDF) cards refer to spinel lattices differing in the level of inversion; the X-ray diffraction (XRD) patterns they carry are similar
Summary
Magnesium gallate (MgGa2O4) is a stiff, refractory (melting point ~1930 °C ), double oxide, with an intermediate band gap value (~4.9 eV) that makes it possible to produce both insulator and conductive variants, as well as being resistant to decomposition until close to its melting point [1]. For applications and spectral studies on transparent MgGa2O4, only single crystals are available currently, to the best of our knowledge. It is worth noting that because the material is cubic and resistant to decomposition, it can be obtained in principle, in polycrystalline (ceramic) form by, for example, powder compact sintering. The incentive to use such an option is that this type of fabrication is significantly simpler and less costly than single crystal growing [8]. In the research described here, our main objective was to establish an MgGa2O4 ceramic fabrication procedure, based on pulsed electric current sintering (PECS), that would allow us to obtain transparent parts. Because of the relevance (noted above) for TM cation spectroscopy of the material, we investigated the spectral (optical) behavior of the Ni-doped transparent magnesium gallate ceramics. Its potential use as a lasing ion (at temperatures < 100 K) increased our interest in this dopant [12,13,14]
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