Chalcopyrite-type Compounds Research Articles

Modulating the optoelectronic and thermoelectric properties of chalcopyrite AgXTe2 (X: Ga, In) via in-plane biaxial strain

The influence of biaxial-in-plan strain on optoelectronic and thermoelectric characteristics of AgXTe2 (X: Ga, In) chalcopyrite type compound has been investigated using density function theory base on full potential linear augmented plane wave technique. The generalized Perdew-Burke-Ernzerhof gradient approximation (PBEsol GGA) is used to optimize unit cell and the Tran-Blaha modified Becke-Johnson (TB-mBJ) approach is employed to improve the electronic, optical and thermoelectric properties. The effects of biaxial strains of the tensile (1%, 2%, 3%) and compression (-1%, -2%, -3%) have been calculated along with contribution of two cations (Ga and In). The calculated band gap of AgGaTe2 and AgInTe2 without strain is 1.17 and 1.13 eV that decreases with applied tensile strain and increases with compressive strain. Without strain maximum absorption is obtained at 1.3 eV and 1.1 eV AgGaTe2 and AgInTe2 respectively, however, tensile and compressive strain shows red and blue shift accordingly. The increase in flatness of valance band with compressive strain results in a large Seebeck coefficient due the large hole effective mass. This identifies AgGaTe2 as a possible efficient thermoelectric material. Consequently, the present study is very useful for developments of desired characteristics by applying strain for optoelectronic and thermoelectric devices.

Nonlinear Optical Crystals for Second Harmonic Generation

Some important nonlinear optical crystal families in three spectral regions (DUV-FIR) have been discussed with reference to their anionic groups. In the M–F–IR region iodides and chalcopyrite-type compound, in the Vis-NIR region sillenites, perovskites and KTP families and in the DUV region borate compound have been investigated. Their important optical and structural factors have been presented. As moderate birefringence increases phase matching wavelength range, the birefringence measurement has been described in more detail. Recent research has focused on optimizing the structure for obtaining high-LDT crystals in the M–F–IR region and removing the layering structure to achieve large-sized crystals in the DUV region. The entry of small ions in the first case and the replacement of stronger interlayer ions such as Ba and Sr, which have a stronger bond with double layer in the second case, are the solutions presented. Combination of two polarized structure units in such a way to make constructive superposition is followed to rise SHG efficiency. The crystals with 3D network are promising for large size growth.

The Effect of Copper Vacancies on the Anion Position of Chalcopyrite Type CuGaS2

The prediction of structural parameters and optoelectronic properties of compound semiconductors is very important. However, calculations often neglect chemical variability and structural defects. In chalcopyrite type semiconductors one of the major defects are copper vacancies (VCu). The four cation neighbors of the anion determine its position in the chalcopyrite type structure expressed by the Wyckoff position 8d (x, 1/4, 1/8). Intrinsic point defects like VCu and anti‐sites may cause variations of the anion position in the middle of the cation tetrahedron, especially in the anion position parameter x. For stoichiometric chalcopyrite type compounds a formalism according to the principle of conservation of tetrahedral bonds (CTB) can be applied to calculate the anion position parameter, but it fails in the case of off‐stoichiometric chalcopyrites. This case study of chalcopyrite type CuGaS2 and Mn‐substituted GuGaS2 shows that the experimentally determined anion position parameter x deviate from values calculated by CTB approach. The systematic investigation of off‐stoichiometric CuGaS2 and Mn‐substituted GuGaS2 demonstrates the effect of copper vacancies on the average radii of the cation sites (Wyckoff positions 4a and 4b) as well as on the anion position parameter x. By applying an elaborated CTB approach implementing copper vacancies an agreement between experimental and calculated anion position parameter x can be obtained.

Pressure Effect of the Vibrational and Thermodynamic Properties of Chalcopyrite-Type Compound AgGaS₂: A First-Principles Investigation.

To explore the structural, vibrational, and thermodynamic properties of the chalcopyrite-type compound AgGaS2 under pressure, we applied hydrostatic pressure to the relaxed compound based on the first principles calculation and quasi-harmonic approximation. The structural parameters, including lattice constants and bond lengths decrease monotonically with the increasing pressure. The phonon dispersion curves under various pressures reveal the structural phase transition of chalcopyrite-type compound AgGaS2 at about 4 GPa. The intrinsic mechanism of thermal conductivity for the chalcopyrite-type compound AgGaS2 has been shown with phonon anharmonicity. The frequencies of the optical phonons at the center point Γ of the first Brillouin zone were calculated with the longitudinal optical–transverse optical (LO–TO) splitting mode. The dependence of the frequencies of the optical phonons on the pressure provides the information for the Raman spectroscopic study under high pressure. The pressure dependence of the Grüneisen parameters indicates that the instability of chalcopyrite-type compound AgGaS2 is associated with the softening of the acoustic phonon modes at around the center point Γ. The thermal conductivity for chalcopyrite-type compound AgGaS2 could be reduced by applying external pressure. The various thermodynamic properties, such as the Helmholtz free energy, entropy, and heat capacity, at different temperatures and pressures were discussed and analyzed based on the phonon properties.

Antiferromagnetic half metallicity in codoped chalcopyrite semiconductors Cu([formula omitted])Se2 (A and B are 3d transition-metal atoms)

Electronic structures and magnetic properties of group I–III–VI2 chalcopyrite-type compounds Cu(Al1−2xAxBx)Se2 are calculated using the Korringa–Kohn–Rostoker Green's function method, where A (Ti, V, Cr, Mn) and B (Fe, Co, Ni) are 3d transition metal atoms, and x is atomic concentration. We found that codoping of Cr–Co and V–Ni pairs at Al site of host CuAlSe2 exhibit antiferromagnetic (AF) half metallicity with low Curie temperature (TC). The AF half metallic property is supported by nullified net magnetic moment and compensated density of states in the minority spin direction. On the other hand, codoping of Cr–Ni, Mn–Co, V–Co, and Ti–Co pairs at Al site of host CuAlSe2 manifest ferrimagnetic half metallicity with a small net magnetization and keeping antiparallel local spin moments. In Mn–Co case TC is close to room temperature. Besides, Cr–Fe, V–Fe, and Ti–Ni codoping cases lead to an instable magnetic ordering and therefore obtain a disordered local moment (spin-glass like) state.

Lattice Dynamics of Chalcopyrite Type Compounds Part IV. Calculations of TO Phonon Modes in a Reduced Rigid Ion Model

The lattice dynamics of 12 chalcopyrite type compounds CuAlS 2, CuGaS 2, CuInS 2, AgGaS 2, AgGaSe 2, AgInSe 2, ZnSiP 2, ZnGeP 2, CdSiP 2, CdGeP 2, CdSnP 2, and CdGeAs 2, have been investigated based on a 5-parameter model involving two short range stretching force constants, an interaction constant, and the effective dynamic charges of the cations. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.

Lattice Dynamics of Chalcopyrite Type Compounds. Part III. Rigid Ion Model Calculations

The lattice dynamics of 12 chalcopyrite type compounds CuAlS2, CuGaS2, CuInS2, AgGaS2, AgGaSe2, AgInSe2, ZnSiP2, ZnGeP2, CdSiP2, CdGeP2, CdSnP2, and CdGeAs2 have been investigated based on a rigid ion model. As the anisotropy of the dynamic charges is not very pronounced the calculations were done assuming isotropic charges. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.

Lattice Dynamics of Chalcopyrite Type Compounds. Part III. Rigid Ion Model Calculations

The lattice dynamics of 12 chalcopyrite type compounds CuAlS2, CuGaS2, CuInS2, AgGaS2, AgGaSe2, AgInSe2, ZnSiP2, ZnGeP2, CdSiP2, CdGeP2, CdSnP2, and CdGeAs2 have been investigated based on a rigid ion model. As the anisotropy of the dynamic charges is not very pronounced the calculations were done assuming isotropic charges. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.

Lattice Dynamics of Chalcopyrite Type Compounds. Part II. Calculations in a Short Range Force Field Model

The lattice dynamics of 12 chalcopyrite type compounds CuAlS 2 , CuGaS 2 ,CuInS 2 , AgGaS 2 , AgGaSe 2 , AgInSe 2 , ZnSiP 2 , ZnGeP 2 , CdSiP 2 , CdGeP 2 , CdSnP 2 , and CdGeAs 2 have been investigated based on 4 different short range force constant models. In all models a set of different solutions can be obtained which can be distinguished by their force constant patterns. For a comparison of the calculated force constants it is therefore necessary to use the data of the comparable minima. From the set of solutions one is selected by physical reasoning and complete results for a model with 8 force constants are given for this minimum for all 12 compounds. The calculated force constants, normal co-ordinates and potential energy distributions are compiled and discussed.

Lattice Dynamics of Chalcopyrite Type Compounds. Part I. Vibrational Frequencies

To obtain a sound basis for calculations of the lattice dynamics of chalcopyrite type compounds the literature data for the vibrational frequencies of 14 chalcogenides and 8 pnictides crystallizing in this structure are critically analysed. This is done by introducing frequency ratios of those frequencies which can be derived from zone centre or zone boundary vibrations of the sphalerite lattice presuming similar bonding and normal co-ordinates in all compounds investigated. Based on the reliable spectra vibrational frequencies have been calculated for those compounds which have not yet been investigated or for which the results given in the literature are uncertain.

The anisotropy of the thermal expansion in the AgInC2VI chalcopyrite-type compounds from the X-ray diffraction data

The lattice parameters a and c as well as the thermal expansion coefficient for different directions in the AgInS2, AgInSe2, and AgInTe2 chalcoyprite-type compounds are determined as a function of temperature in the range from 80 to about 700 K using a X-ray diffractometry technique. For all three compounds an anisotropy is found between the axial thermal expansion coefficients with the positive coefficient along the a-axis and the negative coefficient along the c-axis. The absolute value of the temperature coefficient αc/a = α∥ – α⊥ of the axial ratio and the mean linear thermal expansion coefficient are the greatest for AgInS2 and the smallest for AgInTe2. [Russian Text Ignored].

Lattice thermal expansion of silver indium disulphide

Lattice parameters of chalcopyrite type compound silver indium disulphide (AgInS2) were determined as a function of temperature by the x-ray method in the temperature range 28 to 685°C. Using these data, the coefficients of thermal expansion,a ⊥ anda ‖, were evaluated by a graphical method. The temperature dependence ofa ⊥ anda ‖ is represented by a suitable equation. The anisotropic thermal expansion of AgInS2 is explained in terms of the thermal expansion of the Ag-S and In-S bonds of the AgInS2 lattice.

Infrared Luminescence of Fe3+ in CuGaS2 and CuAlS2

A sharp luminescence line due to the crystal-field transition ( 4 T 1 – 6 A 1 ) of Fe 3+ in the tetrahedral symmetry is observed for the first time in iron-doped I-III-VI 2 chalcopyrite type compounds, CuGaS 2 and CuAlS 2 . The peak energy is 4,942 cm -1 and 5,804 cm -1 respectively. These values are rather small as compared to those in many ferric oxides in which the excitation energy of 4 T 1 in octahedral symmetry is observed around 10,000 cm -1 . The Zeeman effect is also observed and is explained quantitatively by the use of the ligand field theory: We find that g ⊥ of the lowest excited state is zero and the spin-orbit parameter 18 cm -1 .

Thermoelectric properties of some chalcopyrite-type compounds

Thermoelectric properties of some chalcopyrite-type compounds