arXiv subjects

Mrinmay Sahu

Publications and source records attributed to Mrinmay Sahu.

15 recordsLinked to original sources

arXiv2026

Pressure induced structural phase transition and magneto-elastic coupling in Eu doped LaCrO$_3$

In this study, we have carried out a detailed high pressure investigation on 5$\%$ Eu doped LaCrO$_3$ (ELCO) using synchrotron X-ray diffraction (XRD), micro Raman spectroscopy, and low-temperature magnetization measurements to correlate the structural and magnetic properties under pressure. The high pressure XRD reveals the orthorhombic to rhombohedral structural phase transition around 10.6 GPa. The high pressure Raman data corroborate this result and indicate that the lattice instabilities associated with the low-frequency soft modes play a crucial role in driving this transition. In addition, a pronounced anomaly in the Raman shift and integrated intensity of several Raman modes is observed around 4.5 GPa. By combining the low-temperature magnetization measurements with the anomalies observed in the XRD and Raman data and by comparing with the similar results in LaCrO$_3$ (LCO), a pressure-induced change in the magnetic ground state to antiferromagnetic ordering is predicted.

cond-mat.str-el↗

arXiv2026

Coupled plastic strain- and stress-induced phase transformations and microstructure evolution in Fe-7%Mn alloy in a dynamic rotational diamond anvil cell

Studies of severe plastic deformation (SPD), microstructure evolution, and plastic strain-induced phase transformations (PTs) are crucial for various fundamental and applied disciplines and phenomena. However, they are performed either quasi-statically or at low strain rates and pressures. Here, in situ experiments in a dynamic rotational diamond anvil cell (dRDAC) on SPD and BCC<->HCP PTs at pressures up to 27.6 GPa, rotation rates up to 1,500 RPM, and strain rates up to 2,299/s are performed, considering Fe-7%Mn alloy as an example. Strong plastic straining leads to a unique mechanism and kinetics with simultaneous direct and reverse PTs, which has not been studied for any material. For quasi-static loading, we determine the kinetic parameters for strain-induced direct-reverse PTs and the stationary volume fraction $c$ versus pressure. During torsion at 1,000 and 1,500 RPM, $c$ does not change. After torsion stops, 51 minutes later, it increases by 31% at 1,000 RPM and $c$->0, 7 minutes later at 1,500 RPM. These findings contradict the general wisdom that strain-induced PTs occur only during straining and are governed by strain, independent of time; they reveal an alternative mechanism. It is revealed that the crystallite size of ~28(6) nm, microstrain ~0.0035(8), and dislocation density ~1.3(6)x$10^{15}$/$m^2$ in the HCP phase are steady during static compression and dynamic torsion, during and after the PT, and after torsion. These parameters are independent of pressure, plastic strain tensor, its path, strain rates, and $c$. The results obtained open fundamental research on combined strain- and stress-induced PTs and microstructure evolution under dynamic SPD and high pressure, with various important applications.

cond-mat.mtrl-sci↗

arXiv2026

Pressure induced Electronic and Structural Transition in Ba$_2$NiTeO$_6$

This study explores the pressure evolution of the double perovskite Ba$_2$NiTeO$_6$ by employing experimental and computational techniques. For the study of structural and vibrational properties, synchrotron X-ray diffraction (XRD) and micro-Raman spectroscopic experiments at high-pressures were carried out. As a complementary study, DFT simulations of the structural properties as a function of pressure were performed to support and explain the experimental findings. Furthermore, the electronic and magnetic properties as a function of pressure were investigated using DFT. Our study reveals a structural phase transition from a rhombohedral $R\bar{3}m$ to a monoclinic $C2/m$ phase at high pressure, accompanied by a significant increase in bulk modulus. Certain anomalies were observed in Raman mode frequencies at lower pressures of about 1 GPa, indicating changes in the electronic structure with a modification from direct to indirect bandgap in the sample. A minimum in the Raman mode full-width-half-maximum (FWHM) at about 11 GPa, coincides with an increase in ordering in the sample, indicated by a drop in the distortion index of Ni-O$_6$ octahedra as well as a discontinuity in the $c/a$ ratio.

cond-mat.mtrl-sci↗

arXiv2026

Pressure-Induced Martensitic Phase Transformation and Microstructure Evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ Alloy

The Fe-Mn-based alloys are receiving immense attention due to their applications in the third generation of advanced high-strength steels, owing to their high strength and ductility. A detailed in situ high-pressure structural phase transformation and microstructural evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ alloy has been performed using the axial synchrotron X-ray diffraction technique. The ambient BCC phase of $\text{Fe}\text{-}7\%\text{Mn}$ undergoes pressure-driven structural PT to the HCP phase at 11.4 GPa. Both BCC and HCP phases coexist up to 15.9 GPa; thereafter, they transform into a pure HCP phase, which remains stable up to the maximum pressure of 30.3 GPa. The XRD study reveals that the $(110)_{\mathrm{b}}$ dense crystallographic plane of the BCC lattice transforms into a densely packed $(002)_{\mathrm{h}}$ peak of the HCP lattice following the orientational relationship $(110)_{\mathrm{b}} \parallel (0001)_{\mathrm{h}}$ via diffusionless $ \mathrm{Burger's} $ martensitic crystallographic PT pathway. The evolution of crystallite size and microstrain with pressure shows a distinct change during the structural PT. The microstrain exhibits a sharp anomaly at around 10 GPa, suggesting that the microstructural changes precede the structural PT.

cond-mat.mtrl-sci↗

arXiv2025

Temperature and Pressure Dependent Vibrational Properties of Pristine and Doped Vacancy-Ordered Double Perovskite

Understanding lattice dynamics and structural transitions in vacancy-ordered double perovskites is crucial for developing lead-free optoelectronic materials, yet the role of dopants in modulatingthese properties remains poorly understood. We investigate the vibrational and optical properties of pristine and Antimony(Sb)-doped Cs$_2$TiCl$_6$ vacancy-ordered double perovskite through temperature-dependent Raman spectroscopy (4-273 K), high-pressure studies (0- \~30 GPa), ambient powder XRD, and photoluminescence measurements. Sb doping improves phase purity, reducing impurity-related Raman modes present in pristine samples. Most notably, Sb-doped samples exhibit an anomalous Raman mode M$_1$ appearing exclusively below 100 K at 314-319 cm$^{-1}$, accompanied by changes in the temperature coefficient $χ$ and anharmonic constant $A$ across this threshold. This behavior is absent in pristine Cs$_2$TiCl$_6$. While these observations suggest possible structural changes at low temperature, the origin of the M$_1$ mode remains unclear and may arise from disorder-activated vibrations, symmetry breaking, or dopant-induced local distortions. Low-temperature structural characterization is needed to confirm the nature of this transition. Photoluminescence shows broad self-trapped exciton emission at 448 nm with broader FWHM in Sb-doped samples (164.73 nm) compared to Bi-doped samples (138.2 nm), consistent with enhanced structural disorder. High-pressure Raman measurements reveal continuous mode hardening to 30 GPa with no phase transitions. These results demonstrate that Sb doping modulates the vibrational properties of Cs$_2$TiCl$_6$, though further investigation is required to establish the underlying mechanisms.

cond-mat.mtrl-sci↗

arXiv2025

Pressure induced ferromagnetic to antiferromagnetic phase transition in transition metal chalcogenide Cr$_{3}$Te$_4$

We have carried out a detailed high-pressure investigation on the strongly correlated transition metal chalcogenide $Cr_{3}Te_4$ using Raman spectroscopy and XRD, which is ferromagnetic and metallic at ambient conditions. We find that the monoclinic structure remains stable up to 30 GPa, the highest pressure studied. The Cr-Te bond length and octahedral volume decrease drastically up to 7.6 GPa pressure. The $A_{1g}$ Raman mode shows a red shift up to 7.6 GPa, and the $E_g$ Raman mode shows a sudden drop around the same pressure. Further low-temperature Raman spectroscopic investigation shows that the Raman modes soften at the ferromagnetic to antiferromagnetic phase transition. This suggests a change in the magnetic ordering at high pressure. Our Density Functional Theory (DFT) calculations reveal the change in magnetic ground state from ferromagnetic state to antiferromagnetic state above 7.6 GPa pressure, corroborating our experimental result.

cond-mat.str-el↗

arXiv2025

Pressure-Induced Volume Collapse and Metallization in Inverse Spinel Co$_2$TiO$_4$

The structural, vibrational, electronic, and magnetic properties of inverse spinel $Co_2TiO_4$ (CTO-Sp) under high-pressure (HP) conditions are systematically investigated using X-ray diffraction, Raman spectroscopy, in situ optical microscopy, and first-principles density functional theory (DFT) calculations. At ambient conditions, CTO-Sp exhibits a cubic phase with a space group $Fd\bar{3}m$, and it undergoes two notable structural phase transitions at HP. The first transition, occurring at approximately 7.3 GPa, leads to the tetragonal-$I4_1/amd$ phase with minimal alteration in unit cell volume. {The second transition takes place near 17.3 GPa, where two orthorhombic phases emerge and coexist above this pressure.} This second structural transition corresponds to a first-order phase transition involving a significant reduction in unit cell volume of approximately 17.5$\%$. The bulk compressibility of CTO-Sp and its HP post-spinel phases is almost equal to the average polyhedral compressibility within each phase. DFT calculations reveal a high-spin to low-spin transition, accompanied by the collapse of local magnetic moments in the $Cmcm$ orthorhombic phase, leading to the sample's pressure-induced metallization.

cond-mat.mtrl-sci↗

arXiv2025

Soft mode induced structural phase transition in Ba$_2$ZnTeO$_6$ at high pressure

In this paper, we present a thorough investigation of vibrational, structural, and electronic properties of perovskite-type rhombohedral Ba$_2$ZnTeO$_6$ (BZTO) under systematic application of pressure. To carry out the analysis, we have performed pressure-dependent Raman spectroscopic measurements, synchrotron XRD, and density functional theory-based calculations. At ambient conditions, BZTO stabilizes in $R\bar{3}m$ space group, which under pressure undergoes a structural transition to a monoclinic phase with space group $C2/m$ at around 18~GPa. In-depth Raman analysis reveals softening of a phonon mode E$_g$ ($\sim $ 28cm$^{-1}$) leads to the structural phase transition. First principle DFT calculations also indicate that the doubly degenerate soft mode associated with the in-phase TeO$_6$ octahedral rotation drives the structure to a lower symmetry phase $C2/m$.

cond-mat.mtrl-sci↗

arXiv2023

Pressure-induced softening in bulk modulus due to magneto-elastic coupling in Nd$_2$CoFeO$_6$ double Perovskite

Double perovskite oxide materials have garnered tremendous interest due to their strong spin-lattice-charge coupling. Interesting in their own right, rare-earth-based DPOs have yet to be subjected to high-pressure studies. In this paper, we have investigated the structural response of Nd$_2$CoFeO$_6$ to pressure by XRD and Raman spectroscopic measurements. From XRD data, we have observed pressure-induced structural transition from the orthorhombic phase to the monoclinic phase at about 13.8~\si{\giga\pascal}. An anomalous increase in compressibility at a much lower pressure($\sim$1.1~\si{\giga\pascal}) is seen where no structural transition occurs. At about the same pressure, a sudden drop in the slope of Raman modes is observed. Further investigation at low temperatures reveals that the B$_g$ Raman mode is strongly affected by magnetic interactions. Additional high-pressure Raman experiments with the application of a magnetic field indicated that the mentioned anomaly around 1.1~\si{\giga\pascal} can be explained by a high-spin to low-spin transition of Co$^{3+}$.

cond-mat.mtrl-sci↗

arXiv2023

High pressure ferroelectric-like semi-metallic state in $Eu-$doped $BaTiO_3$

We have conducted a detailed high-pressure (HP) investigation on $Eu-$doped $BaTiO_3$ using angle-resolved x-ray diffraction, Raman spectroscopy, dielectric permittivity and dc resistance measurements. The x-ray diffraction data analysis shows a pressure-induced structural phase transition from the ambient tetragonal to the mixed cubic and tetragonal phase above 1.4 GPa. The tetragonality of the sample due to the internal deformation of the $TiO_6$ octahedra caused by charge difference from Eu doping cannot be lifted upon by pressure. Softening, weakening, and disappearance of low-frequency Raman modes indicate ferroelectric tetragonal to the paraelectric cubic phase transition. But the pressure-induced increase in the intensity of [E(LO), A1(LO)] and the octahedral breathing modes indicate the local structural inhomogeneity remains in the crystal and is responsible for spontaneous polarization in the sample. Low-frequency electronic scattering response suggests the pressure-induced carrier delocalization, leading to a semi-metallic state in the system. Our HP dielectric constant and dc resistance data can be explained by the presence of pressure-induced localized clusters of microscopic ferroelectric ordering. Our results suggest HP phase coexistence leads to a ferroelectric-like semi-metallic state in $Eu-$doped $BaTiO_3$ under the extreme quantum limit.

cond-mat.mtrl-sci↗

arXiv2023

Synthesis and EOS study of orthorhombic (Fe,Ni)$_{7}$(C,Si)$_{3}$ and its importance as a possible constituent of Earth's core

We have synthesized an orthorhombic phase of nickel and silicon doped Fe$_{7}$C$_{3}$ at high-pressure and high temperature using a laser-heated diamond anvil cell. The synthesized material is characterized using X-ray diffraction (XRD), Raman spectroscopy, and Transmission Electron Microscopy (TEM) measurements. High-pressure XRD measurement at room temperature up to around 121 GPa is performed. The anomaly observed in the pressure evolution of unit cell volume around 79 GPa along with a slight elastic softening might be associated with a magnetic transition present in the material. The estimated bulk modulus shows a higher value due to the presence of less compressible nickel in the material. Density at core condition is calculated from the thermal pressure corrected equation of state (EOS), which gives an excellent match with the PREM data.

cond-mat.mtrl-sci↗

arXiv2022

Role of electron and hole doping in NdNi1_xVxO3 Nanostructure

Neodymium nickelate, NdNiO3 attracts attraction due to the simultaneous occurrence of several phase transitions around the same temperature. The electronic properties of NdNiO3 are extremely complex as structural distortion, electron correlation, charge ordering, and orbital overlapping play significant roles in the transitions. We report the effects of electron and hole injection via doping a single 3d metal, V, in the NdNiO3 nanostructures to understand the variations in the electronic properties without any structural distortion. A reversible resistivity modulation more than five orders of magnitude via hole doping and complete suppression of metal to insulator transition via electron doping is observed along with the switching of major charge carriers. The modulation of electronic properties without any structural distortion and external strain opens up new directions to consider the NdNi1_xVxO3 nanostructures applicable as emerging electronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Structural and electronic phase transitions in Zr$_{1.03}$Se$_{2}$ at high pressure

A detailed high pressure investigation is carried out using x-ray diffraction, Raman spectroscopy and low temperature resistivity measurements on hexagonal ZrSe$_{2}$ having an excess of 3 at.\% Zr. Structural studies show that the sample goes through a gradual structural transition from hexagonal to monoclinic phase, with a mixed phase in the pressure range 5.9 GPa to 14.8 GPa. Presence of a minimum in the $c/a$ ratio in the hexagonal phase and a minimum in the full width half maximum of the $A_{1g}$ mode at about the same pressure indicates an electronic phase transition. The sample shows a metallic characteristic in its low temperature resistivity data at ambient pressure, which persist till about 5.1 GPa and can be related the presence of slight excess Zr. At and above 7.3 GPa, the sample shows a metal to semiconductor transition with the opening of a very small band gap, which increases with pressure. The low temperature resistivity data show an upturn, which flattens with an increase in pressure. The phenomenological analysis of the low temperature resistivity data indicates the presence of Kondo effect in the sample, which may be due to the excess Zr.

cond-mat.str-el↗

arXiv2021

Pressure driven re-entrant magnetoelectric transition in honeycomb $Fe_{4}Nb_{2}O_{9}$

A detailed high pressure investigation is carried out on $Fe_4Nb_2O_9$ using angle resolved x-ray diffraction and Raman spectroscopy measurements. We find a structural transition from the ambient trigonal phase to a monoclinic phase above 8.8 GPa. The structural transition is assumed to be driven by a large distortion of $Nb-O_6$ octahedra as seen from x-ray diffraction analysis and a large pressure dependence of $Nb-O_6$ octahedra breathing Raman mode. Anomalous behaviour of Raman modes and increase in the phonon life time at the phase transition pressure indicate a trigonal paramagnetic phase to a monoclinic antiferromagnetic state above 8.8 GPa. Decrease in the diffusive scattering rate of low frequency electronic contribution contradicts the results of decrease in intensity of high frequency electronic response and excludes the phenomenon of insulator to metal transition. Instead the enhancement of the intensity of the Raman modes till about 8.8 GPa indicate a large change in ferroelectric polarization of the sample indicating pressure induced re-entrant magentoelectric effect in $Fe_4Nb_2O_9$.

cond-mat.mtrl-sci↗

arXiv2020

High Pressure Structural Investigation on Lead-Free Piezoelectric $0.5Ba(Ti_{0.8}Zr_{0.2})O_3$-$0.5(Ba_{0.7}Ca_{0.3})TiO_3$

The solid solution $0.5Ba(Ti_{0.8}Zr_{0.2})O_3$-$0.5(Ba_{0.7}Ca_{0.3})TiO_3$ (BCZT) has become a promising member of the lead-free piezoelectric materials because of its exceptionally high piezoelectric properties. In this study, we focus on studying pressure-dependent Raman spectroscopy, powder x-ray diffraction and dielectric constant measurements on BCZT. The data show several structural transitions are present, where the system from ambient mixed phase (tetragonal, {\it {P4mm}}+ orthorhombic {\it {Amm2}}) transforms into single phase ({\it {P4mm}}) at 0.26 GPa, then converts into cubic phase ({\it {Pm3m}}) at 4.7 GPa followed by another possible structural re-ordering around 10 GPa. Although there have been a lot of unanimity with the ambient crystallographic state of BCZT, our analysis justifies the presence of an intermediate orthorhombic phase in the Morphological Phase Boundary (MPB) of BCZT phase diagram. The transformation tetragonal to cubic is indicated by the Raman mode softening, unit cell volume change and the $(Ti/Zr)O_6$ octahedra distortion, which coincides with the well-known ferroelectric-paraelectric transition of the system. The sudden drop in the dielectric constant value at 4.7 GPa also confirms the loss of ferroelectric nature of the BCZT ceramic.

cond-mat.mtrl-sci↗