A.O. Fedorchuk

X-ray photoelectron spectrum, X-ray diffraction data, and electronic structure of chalcogenide quaternary sulfide Ag2In2GeS6: experiment and theory

We report measurements of the X-ray diffraction and X-ray photoelectron spectrum on single crystals of Ag2In2GeS6. We also present first principles calculations of the band structure and density of states using the state-of-the-art full potential augmented plane wave method with different possible approximation for the exchange correlation potential. In this paper, we make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. The theoretical results of the density of states are in reasonable agreement with the X-ray photoelectron spectroscopy (VB-XPS) measurements with respect to peak positions. The calculated density of states shows there is a strong hybridization between the states in the valence and conduction bands states. We have calculated the electron charge density distribution in the (100) and (110) planes. In the plane (100), there exists Ag, In, and S atoms, while the plane (110) Ag, S, and Ge atoms are present. The bonding properties are obtained from the charge density distributions. The calculation show that there is partial ionic and strong covalent bonding between Ag–S, In–S, and Ge–S atoms depending on Pauling electro-negativity difference of S (2.58), Ge (2.01), Ag (1.93), and In (31.78) atoms.

Formation of intermediate solid solutions in the quaternary exchange system Cu(In,Ga)(S,Se)2–2Cd(S,Se)

While record solar cells based on Cu(In,Ga)Se2 (CIGS) absorbers exhibit the highest conversion efficiencies among all thin film photovoltaic technologies, the structural nature of the electronically favourable heterojunction CIGS–CdS is still debatable. Here, we present an investigation of the phase equilibria in the full Cu(In,Ga)(S,Se)2–2Cd(S,Se) quaternary exchange system at the selected annealing temperature of 870 K in order to reveal the formation of intermediate solid solutions. There are three single phase regions in the system: the chalcopyrite α-solid solution based on Cu(In,Ga)(S,Se)2, the wurtzite β-solid solution of Cd(S,Se), and the intermediate γ-solid solution existing in a zinc blende structure. The γ-phase has a broad homogeneity range and crystallizes in the cubic space group F3m with a statistical distribution of metal atoms in the cation sub-lattice.

β-BaTeMo2O9 microcrystals as promising optically operated materials

Studies of optical second harmonic generation (SHG) at fundamental wavelength of 1064xa0nm under photoinducing treatment of monoclinic piezoelectric β-BaTeMo2O9 (β-BTMO) were done. Continuous wave (CW) lasers generating at 808 and 1040xa0nm were used as photoinducing sources. The investigations were performed for the β-BTMO microcrystalline powder samples with grain sizes varying within the 25–300xa0μm range. We showed that depending on the microcrystallites size, the photoinduced changes of the SHG were substantially different depending on number of defects which were controlled by positron annihilation. The photoinduced SHG efficiency was substantially higher for more defective crystallites. The processes are completely reversible; however, their photoinduced time kinetics is very sensitive to the wavelength of the photoinducing CW laser beam. The possible reasons for the observed differences are discussed within a framework of intrinsic defect trapping levels and their interactions with phonon subsystem.

Experimental and theoretical study of the electronic structure and optical spectral features of PbIn6Te10

We present measurements of the optical properties of crystalline PbIn6Te10. The samples are grown in the form of parallelepipeds of size ∼5 × 3 × 0.3 mm3. The absorption coefficient α(hν) shows an exponential behavior with energy in the energy range 0.82–0.99 eV followed by an abrupt increase in the absorption from 1.07–1.13 eV. According to the analysis of the data, the indirect gap is 0.88 eV while the direct gap is 1.05 eV. We have used our own measured X-ray diffraction data of the atomic positions in the unit cell as the input for the first principles calculations. Using the generalized gradient approximation (PBE − GGA) within the full potential linear augmented plane wave (FPLAPW + lo) method, the atomic positions are relaxed so as to minimize the forces acting on the atoms. We have used this relaxed geometry to calculate the electronic structure and related ground state properties using PBE − GGA and a recently modified Becke–Johnson potential (mBJ) and mBJ with spin–orbit coupling (mBJ + soc). The analysis of band energy dispersion shows that the valence band maximum (VBM) is located at Γ symmetry points, while the conduction band minimum (CBM) is situated at the M symmetry point of the first Brillouin zone, resulting in an indirect energy band gap of about 0.5 eV (PBE − GGA), 0.8 eV (mBJ) and 0.5 eV (mBJ + soc). It is clear that mBJ succeeds by a large amount in bringing the calculated energy gap in good agreement with the measured energy gap of 0.9 eV. However the inclusion of spin–orbit coupling modifies strongly the CBM and reduces the band by 0.3 eV. The anisotropy of space charge density distribution is analyzed with respect to the charge density distribution.

Band Structure Simulations of the Photoinduced Changes in the MgB2:Cr Films

An approach for description of the photoinduced nonlinear optical effects in the superconducting MgB2:Cr2O3 nanocrystalline film is proposed. It includes the molecular dynamics step-by-step optimization of the two separate crystalline phases. The principal role for the photoinduced nonlinear optical properties plays nanointerface between the two phases. The first modified layers possess a form of slightly modified perfect crystalline structure. The next layer is added to the perfect crystalline structure and the iteration procedure is repeated for the next layer. The total energy here is considered as a varied parameter. To avoid potential jumps on the borders we have carried out additional derivative procedure.

Photoinduced enhancement of optical second harmonic generation in LiB3O5 nanocrystallites embedded between the Ag/ITO electrodes

It is reported that there is substantial enhancement of the optical second harmonic generation (SHG) at 1064xa0nm Nd:YAG laser wavelength for LiB3O5 nanocrystatllites embedded into the electric field aligned photopolymer oligoetheracrylate matrices. The borate nanocomposite was put between the electrodes containing Ag/ZnO NP with silver sizes 20, 40 and 60xa0nm. We study an influence of the Ag NP sizes on the output SHG. It is clearly seen that only excitation by the green continuous wave 532xa0nm laser with power about 350–400xa0mW with beam diameter about 4xa0mm give significant effect. The latter confirms a principal role of the surface plasmon resonances spectrally overlapped with the nonlinear excitations responsible for the observed changes of the SHG.

Specific Features of Phase Formation and the Crystal Structures of Compounds in the Ternary Tm–Cu–Si System

The methods of X-ray phase diffraction and structural diffraction analyses and, partially, the method of microstructural analysis are used to study the phase equilibria in the ternary Tm–Cu–Si system and plot the isothermal section of the phase diagram of this system at 870°K. The existence of seven ternary compounds at this temperature, namely, Tm3Cu11Si4 , TmCu2Si2 , Tm6Cu8Si8, TmCuSi, TmCu0.5Si1.5 , TmCu0.39–0.09Si1.61–1.91, and TmCu0.05Si1.66 is established. It is shown that solely the TmCu2 binary compound dissolves 5 at.% Si. At the same time, we did not detect any noticeable solubility of the third component in the other binary compounds. The structural parameters are determined for the following ternary compounds: Tm3Cu11Si4 (ST Sc3Ni11Si4 , SG P63 /mmc , PS hP36, a = 8.3898(6), c = 8.6425(7) Å, RB = 0.0606, RF = 0.0442, RP = 0,0351, Rwp = 0.0570, and χ2 = 1.74), TmCuSi (ZrBeSi, P63 /mmc , hP36, a = 4.1399(3), c = 7.1471(7) Å, RB =0.0493, RF = 0.0449, RP = 0.0698, Rwp = 0.0930, and χ2 = 1.98), and TmCu0.5Si1.5 (AlB2 , P6/mmm , hP3, a = 3.9799(3), c = 3.9197(4) Å, RI = 0.0543, RP = 0.0293, and χ2 = 1.01). The specific features of the Tm–Cu–Si system and its relationship with the previously studied R–Cu–Si systems are analyzed.

Investigations of the TlInP2Se6–In4(P2Se6)3 System and its Optical Properties

Abstract The equilibrium phases were investigated and the corresponding phase diagram constructed for the TlInP2Se6–In4(P2Se6)3 system from physical and chemical analyses, namely differential thermal analysis (DTA), X-ray diffraction (XRD), and microstructural analysis (MSA). It was established that this system belongs to the eutectic type and is characterized by the formation of boundary solid phases containing complex compounds. Single crystals of the compounds TlInP2Se6 and In4(P2Se6)3 were grown using the Bridgman method. Both crystals were found to exhibit diffuse reflection spectra and photoinduced dependence of birefringence at various IR wavelengths generated by CO2 laser irradiation. Birefringence properties were investigated using the Senarmont method.

Experimentální a teoretické studie elektronické struktury a optické spektrální charakteristiky PbIn6Te10

We present measurements of the optical properties of crystalline PbIn6Te10. The samples are grown in the form of parallelepipeds of size _5 _ 3 _ 0.3 mm3. The absorption coefficient a(hn) shows an exponential behavior with energy in the energy range 0.82–0.99 eV followed by an abrupt increase in the absorption from 1.07–1.13 eV.