Interatomic interaction aspect of phase transition in AgInS₂ crystals

Abstract

The structural parameters of two modifications of AgInS, are determined. The geometrical model of phase transition is discussed. Crystallochemical comparison reveals the absence in the two modifications of significant differences in atomic interactions. The changes in atomic interaction with the temperature increase and the role of dynamical changes in phase transition are discussed.Onpenenem1 napaMeTpb1 CTPYKTYP ~B Y X Mom@nmautifi AgInS,. PaccMoTpeHa reoMeTpMqeCKaR MOHeJIb (pa30BOr0 nepeXOna. n y T e M KPACTaJIJIOXAMAYeCKOrO CpaBHeHRcI nOKa3aHO OTCYTCTBLl e CyWeCTBeHHbIX pZl3JILlWlfi B Mel KaTOMHOM B3aHMOAefiCTBHH y nByX MOnLl@HHaUHfi. 0 6 c y m n a e~c~ XapaKTep H3MeHeHHfI MelfEaTOMHOrO B3aLlMOnefiCT-Ternary semiconductors AIBIIICX*, the crystallochemical analogues of AIIBV1 compounds ape of interest for use in nonlinear optics and polarization optoelectronics. Unlike other semiconductors of this type AgInS, compound exists in two modifications: low-temperature tetragonal phase (t) and high-temperature orthorhornbic phase (r), being in equilibrium above 620 "C and stable at room temperature. Current paper includes the results of the detailed study of AgInS, structure and mechanism of its phase transition. The structure of r-AgInS, existing ia some other ternary tetrahedral compounds is analogous t o that of wurtzite. The transformation of hexagonal wurtzite cell into orthorhombic one is carried out by the doubling of the base smaller edge of the first in orthogonal setting. The symmetry is redxced to Pna2, ((2:"). Annealing a t 600 "C results in structural transformation but the ordinary single crystal with chalcopyrite-type structure is not yet formed. Weissenberg studies show these crystals to be twins. Twin parts are rotated by 180 "C about each other within one of { 112}t,t planes. This type of twinning of cubic crystals as well as analogous one along (111) is observed in crystal growing of ternary and binary compounds from solution or vapour phase. But the characteristic feature of investigattd AgInS,

Lattice dynamics and related properties of AIBIII and AIIBIV compounds, I. Elastic constants

“…The elastic constants of Table 8 yield a value of Θ XR = 285 K using the approximation of an isotropic solid for an orthorhombic lattice [108]. The most reliable experimental value determined by suitably averaging atomic temperature factors obtained by a structure refinement of orthorhombic AgInS 2 is Θ XR = 158 K [117,126]. The resulting ratio Θ XR (exp)/ Θ XR (calc) = 0.55 is well outside the admitted ratio Θ XR (exp)/ Θ XR (calc) = 0.80 ± 0.09 [92].…”

“…At room temperature the ternary compound AgInS 2 is stable in two different modifications, in the chalcopyrite structure and in the orthorhombic β-NaFeO 2 structure (space group Pna2 1 ) [117,118], a derivative of the wurtzite structure [119]. For the latter, mechanically more stable modification of the compound measurements of the X-ray thermal diffuse scattering intensity at room temperature on appropriately oriented single crystals [120,121] have been used to determine the complete set of the nine independent elastic stiffness constants c ij of an orthorhombic lattice which can be expressed in matrix form as …”

The Anisotropy of Elastic Properties in Orthorhombic Modification of AgInS2 from X-Ray Thermal Diffuse Scattering Data

“…In particular, the relation c b`ca`cc between the principal components of compressibility tensor was found to exist [13]. The largest difference between the b-and c-components was also observed for the thermal expansion coefficients [18], the mean-square dynamic displacements [3,10] and X-ray Debye temperatures [10]. This is connected with the crystal structure feature and orthorhombic distortion in this ternary compound [13].…”

“…The X-ray studies were made on (8 Â 6 Â 6 mm 3 ) single crystals of AgInS 2 , grown by Bodnar and Korzun [2] using the Bridgman method, with the lattice parameters a = 0.70105 nm, b = 0.82773 nm and c = 0.66917 nm and density r = 4.93g/cm 3 . Three sample faces cut parallel to the (100), (010) and (001) planes were used.…”

First principles study in the electronic structures and optical properties of chalcogenide-doped AgInS2

“…Ternary chalcogenide materials have been currently received attention from these scienti c topics because of their e cient technological applications. [1][2][3][4][5][6][7][8][9] AgInS 2 is one of the I-III-VI 2 ternary chalcogenide semiconductors widely used in the active elds of photovoltaic cells, photocatalysis, optoelectronics and nonlinear optics [10][11][12][13]. In addition, AgInS 2 semiconductor is a suitable material to be implemented as visible light absorber layers because of its optimal band gap, high absorption coe cient and low toxicity.…”