arXiv subjects

Pintu Singha

Publications and source records attributed to Pintu Singha.

4 recordsLinked to original sources

arXiv2026

Favorable half-Heusler structure of synthesized TiCoSb alloy: a theoretical and experimental study

The most favorable structure of the synthesized TiCoSb half-Heusler alloy is explored theoretically and experimentally, and the best structure for thermoelectric conversion is reported. Rietveld refinement of the X-ray diffraction data employing four probable structures of the HH alloy is performed to obtain the best fit and identify the crystallized structure. However, microstructural characterization is performed using the energy dispersive X-ray spectroscopy and transmission electron microscopy to reveal the stoichiometry and Bragg reflection planes of the synthesized polycrystalline lattice structure of TiCoSb HH alloy. Theoretical investigation is performed by implementing the first principle calculation using the Full Potential Linearized Augmented Plane Wave method in the Quantum Espresso software package. The most probable structure is explored by estimating the minimum energy at equilibrium volume and electronic structure of the TiCoSb half-Heusler alloy of the four probable structures considered. The theoretical and experimental data are corroborated, and the most probable structure is identified for the crystallized TiCoSb HH alloy. The thermoelectric properties of the most probable structure are estimated.

cond-mat.mtrl-sci↗

arXiv2025

Investigation of Softer Lattice Dynamics in Defect Engineered GeTe Crystals

The impact of Ge vacancies on the low-temperature lattice dynamics of single-crystalline GeTe was investigated through a comparative study of two off-stoichiometric samples: Ge$_{0.8}$Te (S$_1$) and Ge$_{0.88}$Te (S$_2$). X-ray diffraction confirms their highly oriented crystalline nature mainly along the $h0l$ plane, while temperature-dependent Raman spectroscopy reveals pronounced anharmonicity in S$_1$, indicated by stronger three-phonon scattering in the in-plane E-mode. A suppressed Raman feature at $~$ 239 $cm^{-1}$ in S$_2$ suggests fewer disordered GeTe$_{4-n}$Ge$_n$ tetrahedra, correlating with reduced Ge-Ge bonding signatures. Machine-Learned Molecular Dynamics (MLMD) simulations show dominant Te contributions below 100 $cm^{-1}$, while Ge dominates above, particularly influencing the 120 $cm^{-1}$ mode affected by defects at the Ge-site. Complementary calculation of phonon linewidth via MLMD and Temperature-Dependent Effective Potential (TDEP) methods affirm the predominance of three-phonon scattering below 300 K. Specific heat measurements, modeled using Debye-Einstein formalism, show lower Debye temperatures ($θ_D$) of 172.3 $\pm$ 1.5 K in Ge$_{0.8}$Te and 176.6 $\pm$ 1.7 K for Ge$_{0.88}$Te respectively, confirming defect-induced lattice softening. Electrical resistivity analysis further corroborates this, indicating reduced effective phonon frequencies in $S_1$. Thus, our results establish that higher Ge vacancies lead to softer, and hence more anharmonic lattice dynamics in GeTe, with its relevance in designing superior thermoelectric and phase-change memory applications.

cond-mat.mtrl-sci↗

arXiv2023

Transport phenomena of TiCoSb: Defects induced modification in structure and density of states

TiCoSb1+x (x=0.0, 0.01, 0.02, 0.03, 0.04, 0.06) samples have been synthesized, employing solid state reaction method followed by arc menting. Theoretical calculations, using Density Functional Theory (DFT) have been performed to estimate band structure and density of states (DOS). Further, energitic calculations, using first principle have been carried out to reveal the formation energy for vacancy, interstitial, anti-site defects. Detail structural calculation, employing Rietveld refinement reveals the presence of embedded phases, vacancy and interstitial atom, which is also supported by the theoretical calculations. Lattice strain, crystalline size and dislocation density have been estimated by Williamson-Hall and modified Williamson-Hall methods. Thermal variation of resistivity [\r{ho}(T)] and thermopower [S(T)] have been explained using Mott equation and density of states (DOS) modification near the Fermi surface due to Co vancancy and embedded phases. Figure of merit (ZT) has been calculated and 4 to 5 times higher ZT for TiCoSb than earlier reported value is obtained at room temperature.

cond-mat.mtrl-sci↗

arXiv2022

Observation of Griffiths-like phase in the quaternary Heusler compound NiFeTiSn

The quaternary Heusler compound NiFeTiSn can be considered to be derived from the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni. In contrast to Fe2TiSn, which shows a disorder-induced ferromagnetic phase, the ground state of NiFeTiSn is antiferromagnetic with the signature of spin canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by isolated ferromagnetic clusters before attaining the antiferromagnetic state. The Griffiths-like phase is possibly associated with the antisite disorder between Fe and Ti sites as evident from our powder X-ray diffraction study. The compound also shows rather an unusual temperature dependence of resistivity, which can be accounted for by the prevailing structural disorder in the system. NiFeTiSn turned out to be a rare example where a Griffiths-like phase is observed in a semiconducting 3d transition metal-based intermetallic compound with an antiferromagnetic ground state.

cond-mat.str-el↗