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An ab initio study of electronic, mechanical, and piezoelectric properties of the trigonal, tetragonal and cubic phases of lead-free perovskite SnBO3 (B = Ti, Zr, Hf)

2024-01-01T00:00:00Z

Title: An ab initio study of electronic, mechanical, and piezoelectric properties of the trigonal, tetragonal and cubic phases of lead-free perovskite SnBO3 (B = Ti, Zr, Hf) Authors: Lalhriatzuala Abstract: (P4mm) and cubic (Pm̅3̅m) phases of SnBO3 (B Ti, Zr, Hf) oxide perovskite compounds using various functionals namely GGA-PBE, PBE0, HSE06, and B3LYP. From formation energy calculation, trigonal symmetry has been found to be the most stable phase. In the structure optimization, B3LYP estimates the largest volume under trigonal and tetragonal symmetry. However, for the cubic system of SnBO3, SnTiO3 possess the largest volume when using PBE-GGA, while B3LYP estimates the largest in SnZrO3 and both PBE-GGA and B3LYP estimates the same magnitude in SnHfO3. When Ti atom is replaced with either Zr or Hf, a notable shift in the second oxygen atomic coordinate was observed in the tetragonal phase along the z-direction, which impacts the lattice parameters leading to an expansion along the a-axis but with contraction along the c-axis. Structural changes have been found to correspond with electronic transitions. While the electronic transition in SnTiO3 takes place along �→Γ, the transitions in both SnZrO3 and SnHfO3 occurs along �→Z in k space. In the cubic system, SnTiO3 showed an indirect X→Z transition, whereas SnZrO3 and SnHfO3 demonstrated a direct X→X transition. Density of states calculations have revealed that contribution from the B-site atom in the energy states around the conduction band edge is reduced as Ti atom is substituted with Zr atom and subsequently with Hf atom for all the crystal phases. Mechanical stability was consistent across all the compounds in all the calculations with various exchange-correlation functionals considered. Analysis of the mechanical parameters of the trigonal phase of SnBO3 has deduced that only SnTiO3 using hybrid functionals shows brittleness. While only SnHfO3 consistently exhibited a ductile nature throughout the functionals considered in the tetragonal phase, all compounds in the cubic phase were ductile. Interestingly, while the bulk modulus increased sequentially from Ti to Zr and then to Hf when B site atom is substituted in tetragonal structures, SnTiO3 emerged as the most robust system in the cubic phase. In the tetragonal system, when Ti atom in SnBO3 is replaced with either Zr or Hf, the piezoelectric response exhibits massive increase associated with the change in atomic position of the second oxygen atom along the c-axis and the response is also predicted to be highest in SnHfO3.

Surface half metallicity and thermodynamic stability of 001-plane Ti2XSi (X=Mn, Co) Heusler alloys (HAs): A DFT approach

2022-02-28T00:00:00Z

Title: Surface half metallicity and thermodynamic stability of 001-plane Ti2XSi (X=Mn, Co) Heusler alloys (HAs): A DFT approach Authors: Lalhriatzuala Abstract: We breport the surface stability and surface half-metallicity of Ti2XSi (X=Mn/Co) [001] slab with natural TiSi and TiX(X=Mn/Co) terminals from the first principles calculation. We started our calculation from the bulk optimization followed by the electronic and magnetic properties by adopting GGA exchange correlation for treating all electrons interaction. We have also analyzed the surface stability by calculating the surface energies as a function of constituents chemical potentials within the framework of ab-initio thermodynamics. Within the allowed chemical potentials range, TiSi(Ti2MnSi) terminated surface found to be the most energetically favorable thin film while the TiX terminated surfaces show strong molecular attraction. The bulk half metallicity is preserved in TiSi(Ti2MnSi) terminated surface with 100% spin polarization while the other terminal surfaces are metallic. The results of atomic site partial magnetic moments in the surface states along with their corresponding values in the bulk structure are also presented.

Structural, Optical and Electrical Characterization of CdSe Nanorods Synthesized by Solvothermal Process

2023-04-30T00:00:00Z

Title: Structural, Optical and Electrical Characterization of CdSe Nanorods Synthesized by Solvothermal Process Authors: Lalhriatzuala Abstract: CdSe is a direct band gap II–VI compound semiconductor, which can exist in both zinc blende phase and wurtzite phase. Its direct band gap of 1.7 eV divides the solar spectrum into two parts, namely, the “thermal” part with ℎ] < 𝐸 𝑔 and the “optical” one with ℎ] > 𝐸 𝑔, both parts with practically equal radiation energy.

Studies on Spin Orbit Splitting and Dual Mode Phonon Vibrations in ZnSxSe1 x Ternary Alloys Films with Varying Se Concentration

2015-01-01T00:00:00Z

Title: Studies on Spin Orbit Splitting and Dual Mode Phonon Vibrations in ZnSxSe1 x Ternary Alloys Films with Varying Se Concentration Authors: Lalhriatzuala Abstract: ZnSxSe1 x (x = 0, 0.41, 0.51, 0.91, 1) ternary alloy thin films with variable structural, optical and vibrational properties were prepared by thermal evaporation of solvothermally synthesized ZnS-ZnSe nanocomposite powders. The deposited films were uniform and have zinc-blende structure with (111) orientation. Variation of lattice parameter with composition was slightly nonlinear with a bowing parameter of 0.12 A ° . Spin orbit (SO) splitting of the valence band was observed in binary ZnSe and ternary samples with large Se atomic concentration such as ZnS0.41Se0.59 and ZnS0.51Se0.49. The SO splitting energy decreases as the Se atomic concentration in the alloy decreases. Two phonon modes (corresponding to ZnS and ZnSe bonds) behavior were observed in the Raman spectra of the ternary alloys. The observed phonon mode frequencies shifted with changes in Se atomic concentration in agreement with theroretical predictions. Gap mode vibration of Se in ZnS lattice was also observed at 221 cm 1 in the ternary sample with small Se atomic concentration (ZnS0.91Se0.09), which also matches closely with theoretically calculated values.