1. of Aluminumthiophosphate AlPS4
Ab initio investigation of the structural and optoelectronic properties
of Aluminumthiophosphate AlPS4
Ali BENGHIA, Tayeb BENTRIA, Bachir BENTRIA
Laboratoire Physique des Matériaux , Université Amar Telidji de Laghouat. BP 37G Laghouat 03000, Algeria
JOURNÉES D’ÉTUDES SUR LES MATÉRIAUX 14,15 Mai 2014
Abstract
fig.2, we can obtain the transition pressure between phases, which is equal GPa between P222 and I-4. We could say that this phase is the most probable, and we will use it together with the experimental phase P222 in our further
the non-controsymetric crystal AlPS4 have been investigated by means of density functional theory; we calculate structural, elastic; electronic and optical properties for two phases P222 and I-4, because the experimental P222 phase shows fragility in z direction. AlPS4 is semiconductor with indirect band gap (2,5 ~ 3.1) eV with mix covalent/ionic bonds obtained from Mullikan population. The dielectric function analyses show that AlPS4 is transparent starting from 400nm, this material is candidate for nonlinear optics because of his good birefringence (z-x) = -0,133 in the P222 phase.
The ternary chalcophosphates family MPX4 (M:metals, X:S,Se,Te) are known for their important physicochemical properties directed through nonlinear optical application because of their strong respond to the second harmonic generation GSH [1]. Their possibility for reversible phase changement, from the non-controsymmetric to centrosymmetric structure leads us to important technological application in different fields, such as: solar energy conversion [2], semiconductor batteries [3] [4], and non linear optical devices [1].
Moreover, these chalcogenides are used in thermograph IR, optical fibers [5], holography, gas detection, memories storage (DVD). These crystals are also well studied in the development of phase-change random access memory [6].
The first synthesized chalcophosphate of these family are BPS4 and AlPS4, by Weiss Schaefer between (1960, 1963)
Calculations are preformed using DFT [10,11] pseudopotential plane wave method as implemented in Cambridge serial total energy package (CASTEP) [12]. Perdew–Burke–Ernzerhof generalized gradient approximation (GGA –PBE) was used for the exchange-correlation potentials [13]. Ultrasoft pseudopotentials (USP) [14] were used with the following valence electronic configurations: Al : 3S2 3P1; P : 3S2 3P3 ; S : 3S2 3P4 .
The cut off energy is 600eV for P222, I-4, I222; and 700 eV for P21/C. the K point sampling is 6×6×4 ; 6×6×6 ; 8 ×6×6 ; 12×12×6 for P222, I-4, P21/C and I222 respectively.
The structural parameters of AlPS4 were determined using the Broyden–Fletcher– oldfarb–Shenno (BFGS) minimization technique[15]. The tolerance for geometry optimization was set as the difference of total energy within eV/atom.
Phase P Phase I-4
Phase I Phase P21/C
Fig 1. Aluminumthiophosphate AlPS4 in Space group P222, I-4, I222 and P21/C respectively,
P222, this structure shows anomalies ,we can see C33 present negative value which contradicts the criteria of stability
Phase I-4: this phase of AlPS4 shows bonds in all directions , the values C11 , C22 , C33 are in the same order ,
Phase I222: this phase is also improbable, because of its relative fragility relative to the other phases
Phase P21/C: this phase of AlPS4 form bi-dimensional layers parallel to crystallographic plans (b, c).
Band structure, Electron density and Mulliken population
Figure.3 which presents the calculated band structure of AlPS4 in P222 and I-4 phase. The two phases shows indirect
band gap, With band gap energy Egap =2,704 (Y—S) and Egap =2.523eV (X—Z) for in P222 and I-4 phase respectively
Thus the material is semiconductor.
Introduction
Fig.3. Band structure along the principal high-symmetry directions in the Brillouin zone for AlPS4
in phases P222 and I-4 respectively
Computational detail
The type of bonds in this crystal from the Milliken population Table 2 and electron density difference Fig 4.
Is mix bond (ionic/covalent), this bond is close to covalent for P—S and mix close to ionic for Al—S
Results and discussions
Structural, elastic properties and mechanical stability
Optical properties, dielectric Function and refraction indices
Fig 5. Energy variation verse volume of elementary lattice for the four phases
Reflection index have been calculated show that AlPS4 is transparent starting from 400nm with reflection index of 1.7
and 1.8 for P222 and I-4 respectively.
Conclution
We think that this crystal has the ability to change the electronic properties by modifying the conditions that control
the crystallographic structure phase transition. In this study it was shown that in two different phases AlPS4 P222 I-4
and shows different optical and electronic properties
Reference
[1]- In Chung, Doctor Of Philosophy Chemistry Compounds, Michigan State University, 2008, Umi Number:
[5]- Taylor, P. C. Mater. Res. Soc. Bull. 1987, 36.
[12]- M.D. Segall, P.J.D. Lindan, M.J. Probert, C.J. Pickard, P.J. Hasnip, S.J. Clark, M.C. Payne, J. Phys.
Condens. Matter 14 (2002) [13]- J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865.
Contact Information
BENGHIA Ali
Master. Laboratoire Physique des Matériaux, Université de Laghouat, B.P. 37 G, Laghouat - Algérie
Tel: ,
Fig 2. Energy variation verse volume of elementary lattice for the four phases