Anisotropic mechanical properties of Tl4Ag18Te11 compound with low thermal conductivity

*Sürücü, Özge Bayraklı ( Aksaray, Yazar ) *Deligöz, Engin ( Aksaray, Yazar )The anisotropic mechanical properties of Tl4Ag18Te11 compound was investigated elaborately for the first time by using Density Functional Theory calculations with the Vienna Ab-initio Simulation Package in this work. Tl4Ag18Te11 compound was optimized in the I4mm space group and the formation energy was determined as a negative value that is the indication of the experimental synthesizability of this compound. The optimized crystal structure was employed for the calculations of the elastic constants and the obtained values revealed the mechanical stability of Tl4Ag18Te11 compound. The polycrystalline properties were determined such as shear modulus, Poisson's ratio, etc. In addition, the anisotropic elastic properties were presented. The direction dependent sound waves velocities, polarization of the sound waves, enhancement factor and the power flow angle were determined. The thermal conductivity studies were performed and the minimum thermal conductivity (0.259 ​W ​m−1K−1) and the diffusion thermal conductivity (0.202 ​W ​m−1K−1) were calculated. This study illustrates the capability of this compound for the thermoelectric materials

Equiatomic quaternary Heusler compounds TiVFeZ (Z=Al, Si, Ge): Half-metallic ferromagnetic materials

WOS:000679202700002Equiatomic quaternary Heusler compounds (EQHCs) are very promising materials for spintronic applications due to their excellent electronic and magnetic properties. In this study, structural, electronic, magnetic, mechanic, and dynamic properties of TiVFeZ (Z=Al, Si, Ge) EQHCs are investigated. Three nonequivalent structural configurations of α, β, and γ type structures are considered. The γ is defined as the most stable phase for all these compounds and has a half-metallic character. The predicted Curie temperatures of TiVFeAl, TiVFeSi, and TiVFeGe compounds are about 488 K, 256 K, and 306 K, respectively. We also show that TiVFeZ (Z=Al, Si, Ge) have thermodynamic, dynamic, and mechanical stabilities. The presented results reveal that these compounds are potential materials for spintronics applications

Investigation of precursor sequence and post-annealing effects on the properties of Cu2SnZnSe4 thin films deposited by the elemental thermal evaporation

Cu2ZnSnSe4 (CZTSe) thin films were deposited onto soda lime glass substrates by thermal evaporation using the pure elemental sources. The influence of the sequential deposition order of Zn and Sn precursor layers for different evaporation cycles were investigated. In situ annealing at 400 degrees C under Se evaporation was applied to promote conversion of precursor layers to quaternary compound structure and additionally, subsequent post-annealing processes under nitrogen atmosphere at 450 degrees C was carried out to improve the crystalline behavior. The analyses concluded that the substrate temperature kept at 400 degrees C during selenization was not adequate to form homogenous CZTSe structure and as a result of post-annealing treatment, the polycrystalline quaternary CZTSe film structure was obtained. Structural analysis showed that in comparison with the initial Sn precursor layer, the growth process starting with Zn was found to be the preferable method to form better crystalline CZTSe structure. Furthermore, the stacking layer order and annealing processes showed the important effect on the stoichiometry and surface morphology of the films. The optical band gap energies were around 1.10 eV and also from Tauc plots, 1.40 eV was observed due to the admixture of secondary phases. The room temperature resistivity values and hole carrier densities were obtained around 10(-2) Omega cm and 1019 cm(-3), respectively. The mobility values of the samples were found in between 0.51 and 0.75 cm(2) V-1 s(-1)

Deposition of CZTSe thin films and illumination effects on the device properties of Ag/n-Si/p-CZTSe/In heterostructure

Characterization of Cu2ZnSnSe4 (CZTSe) thin films deposited by thermal evaporation sequentially from the pure elemental sources and in-situ post annealing was carried out at 400 C under Se evaporation atmosphere. Another annealing process was applied in nitrogen atmosphere at 450 degrees C to get poly-crystalline monophase CZTSe film structure. XRD analysis together with Raman spectroscopy was used to determine the structural properties. Spectral optical absorption coefficient evaluated from transmission data showed the band gap value of 1.49 eV for annealed film. Electrical measurements indicated that CZTSe thin films have p-type semiconductor behavior with the carrier density and mobility values of 10(-19) cm(-3) and 0.70 cm(2)/(V.s). Illumination effects on the device properties of Ag/n-Si/p-CZTSe/In heterostructure were investigated by analyzing current-voltage(I-V) and frequency dependent capacitance-voltage(C-V) data. Under the illumination, Ag/n-Si/p-CZTSe/In heterostructure showed photodiode behavior having V-oc value of 100 mV and I-sc value of 27.5 mu A. With the illumination, series resistances (R-s), diode ideality factor (n) and barrier height (Phi(b)) decreased and shunt resistance (R-sh) increased. Capacitance value at lower frequency decreased due to the illumination effect. (C) 2017 Elsevier B.V. All rights reserved

Temperature-dependent optical characteristics of sputtered NiO thin films

In this work, nickel oxide thin films were deposited by radio frequency magnetron sputtering technique. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray analysis methods were applied to reveal the structural and morphological properties of sputtered thin films. The XRD pattern of films confirmed the presence of the cubic phase of nickel oxide with the preferential orientation of (200) direction. The surface morphology of thin films was observed as almost uniform and smooth. Optical aspects of sputtered film were studied by employing the room temperature Raman and temperature-dependent transmittance spectroscopy techniques in the range of 10–300 K. Tauc relation and derivative spectroscopy techniques were applied to obtain the band gap energy of the films. In addition, the relation between the band gap energy and the temperature was investigated in detail considering the Varshni optical model. The absolute zero band gap energy, rate of change of band gap energy, and Debye temperature were obtained as 3.57 eV, ? 2.77 × 10–4 eV/K and 393 K, respectively. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature