Order/disorder phenomena in Zn_1−xMn_xGa₂Se₄ordered vacancy compounds: high temperature neutron powder diffraction experiments

Abstract

We present a study of order-disorder phenomena in the series of tetrahedral ordered vacancy compounds Zn1-xMnxGa2Se4 by means of time-of-flight neutron diffraction at high temperature together with dc magnetic susceptibility, Raman spectroscopy, differential thermal analysis and optical absorption experiments. Samples of nominal composition x = 0, 0.24, 0.5, 0.77 and 1 have been studied. An order-disorder phase transition has been detected, with Tc ranging from 472 to 610 ° C, which involves a structural change from a defect chalcopyrite phase, with I4 space group (s.g.) and three different cation sites, to a partially disordered defect stannite, in which Zn, Mn and half of the Ga ions share the 4d site in I42m s.g. Neither the vacancies nor the Ga ions occupying site 2a are involved in the phase transition. An additional ordering process is observed on approaching the phase transition from below, which is attributed to several factors: the activation of cation diffusion at ∼300 ° C, the partially disordered cation distribution exhibited by the as-grown single crystals and the preference of Mn atoms for the 2d crystallographic site in the I4 structure. The reversibility of the phase transition is analysed with the aid of magnetic, optical and Raman experiments.

Optical Absorption and Photoluminescence in Defect-Stannite-Type Semiconductor ZnGa₂Se₄

“…The lattice constants calculated using (112) and (204) peaks are a=5.5 Å and c=10.9 Å. These values agree with those reported by Gutiérrez et al [10]. It should be noted that ZnGa2Se4 had been reported to have either a defect stannite or a defect chalcopyrite structure, and their difference could be hardly distinguished by XRD measurement.…”

AZn4Ga5Se12 (A = K, Rb, or Cs): Infrared Nonlinear Optical Materials with Simultaneous Large Second Harmonic Generation Responses and High Laser-Induced Damage Thresholds

“…All M atoms bond with Se tetracoordinatedly to form [MSe 4 ] tetrahedra, and M–Se bond lengths are in the range of 2.404–2.469 Å, consistent with those of Ba 10 Zn 7 Ga 6 Se 26 (M–Se, 2.406–2.518 Å) and Ba 4 ZnGa 4 Se 10 Cl 2 (Zn–Se, 2.460 Å; Ga–Se, 2.375–2.410 Å) . Se–M–Se bond angles fluctuate from 103.1° to 117.8°, comparable to those of ZnGa 2 Se 4 (∠Se–Ga–Se, 106.5–115.6°) and Na 3 ZnGaSe 4 (∠Se–M–Se, 100.0–118.6°) . The alkali metal A atom is bonding with the 12 surrounding Se atoms (Figure b) with bond lengths of 3.722–3.825 Å (details in Figures S4–S6), which are consistent with those of A-II 4 -III 5 -Se 12 compounds (3.773–3.940 Å) .…”