Publications (54)
Evidence for anomalous structural behavior in CaFe2As2
S. K. Mishra, R. Mittal, P. S. R. Krishna +5
The structural properties of the CaFe2As2 have been investigated by x-ray and neutron powder diffraction techniques as a function of temperature. Unambiguous experimental evidence…
Behavior of Lithium Oxide at Superionic Transition: First Principles and Molecular Dynamics Studies
M. K. Gupta, Prabhatasree Goel, R. Mittal +2
We report studies on the vibrational and elastic behavior of lithium oxide, Li2O around its superionic transition temperature. Phonon frequencies calculated using the ab-initio and…
Synchrotron X-ray Diffraction Study of BaFe2As2 and CaFe2As2 at High Pressures up to 56 GPa: Ambient and Low-Temperatures Down to 33 K
R. Mittal, S. K. Mishra, S. L. Chaplot +9
We report high pressure powder synchrotron x-ray diffraction studies on MFe2As2 (M=Ba, Ca) over a range of temperatures and pressures up to about 56 GPa using a membrane diamond an…
Inelastic neutron scattering and lattice dynamical calculations in BaFe2As2
R. Mittal, Y. Su, S. Rols +6
We report here first extensive measurements of the temperature dependence of phonon density of states of BaFe2As2, the parent compound of the newly discovered FeAs-based supercondu…
Phase stability and structural temperature dependence in sodium niobate: A high resolution powder neutron diffraction study
S. K. Mishra, R. Mittal, V. Yu. Pomjakushin +1
We report investigation of structural phase transitions in technologically important material sodium niobate as a function of temperature on heating over 300-1075 K. Our high resol…
Spin-Lattice Coupling in K0.8Fe1.6Se2 and KFe2Se2: Inelastic Neutron Scattering and ab-initio Phonon Calculations
R. Mittal, M. K. Gupta, S. L. Chaplot +6
We report measurements of the temperature dependence of phonon densities of states in K0.8Fe1.6Se2 using inelastic neutron scattering technique. While cooling down to 150 K, a phon…
Vibrational and thermodynamic properties of high-pressure phases in LiYF_4
A. Sen, S. L. Chaplot, R. Mittal
Possible variations in the dynamical behaviour of LiYF due to its structural changes following several pressure-induced phase transitions are examined by making use of the co…
Phonon dynamics in SrFe2As2 and SrFeAsF parent pnictide compounds: How different/similar when compared to Ca- and Ba-compounds?
R. Mittal M. Zbiri, S. Rols, Y. Su +9
We report detailed measurements of temperature dependence and ab initio lattice dynamical calculations of the phonon density-of-states of two Sr based iron pnictide parent compound…
Neutron Diffraction Reveals the Existence of Confined Water in Triangular and Hexagonal Channels of Modified YPO4 at Elevated Temperatures
S. K. Mishra, R. S. Ningthoujam, R. Mittal +8
We provide experimental evidence for confinement of water molecules in the pores of hexagonal structure of YPO4 at elevated temperatures upto 600 K using powder neutron diffraction…
Spin-Phonon Coupling, High Pressure Phase Transitions and Thermal Expansion of Multiferroic GaFeO3: A Combined First Principles and Inelastic Neutron Scattering Study
M. K. Gupta, R. Mittal, M. Zbiri +4
We have carried out an extensive phonon study on multiferroic GaFeO3 to elucidate its dynamical behavior. Inelastic neutron scattering measurements are performed over a wide temper…
Effect of Hydration and Ammonization on the Thermal Expansion Behaviour of ZrW2O8: Ab-initio Lattice Dynamical Perspective
M. K. Gupta, R. Mittal, Baltej Singh +1
The hydration and ammonization of ZrW2O8 is known to lead to positive and negative thermal expansion behaviour respectively. We report ab-initio calculations to understand this ano…
Lattice vibrations in high-pressure phases of LiYF
A. Sen, S. L. Chaplot, R. Mittal
Possible variations in the dynamical behaviour of LiYF due to its several structural changes under pressure are examined by making use of the complementary techniques of quas…
Phonons and Anomalous Thermal Expansion Behaviour in Crystalline Solids
R. Mittal, M. K. Gupta, S. L. Chaplot
Anomalous thermal expansion behaviour of several open frame-work compounds has been extensively investigated using the techniques of inelastic neutron scattering and lattice dynami…
High-Temperature Phonon Spectra of Multiferroic BiFeO3 from Inelastic Neutron Spectroscopy
M. Zbiri, H. Schober, N. Choudhury +5
We report inelastic neutron scattering measurements of the phonon spectra in a pure powder sample of the multiferroic material BiFeO3. A high-temperature range was covered to unrav…
Phonons and Oxygen Diffusion in Bi2O3 and (Bi0.7Y0.3)2O3
Prabhatasree Goel, M. K. Gupta, R. Mittal +3
We report investigation of phonons and oxygen diffusion in Bi2O3 and (Bi0.7Y0.3)2O3. The phonon spectra have been measured in Bi2O3 at high temperatures up to 1083 K using inelasti…
Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution
Anupinder Singh, Ratnamala Chatterjee, S. K. Mishra +2
The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveal that La rich (BF-LF)-(PT)…
Fast ion diffusion, superionic conductivity and phase transitions of the nuclear materials UO2 and Li2O
Prabhatasree Goel, N. Choudhury, S. L. Chaplot
Lattice dynamics and molecular dynamics studies of the oxides UO2 and Li2O in their normal as well as superionic phase are reported. Lattice dynamics calculations have been carried…
Dynamics of Li-ion in V2O5 Layers from First-Principles Calculations
Baltej Singh, M. K. Gupta, R. Mittal +1
The alkali atoms, due to their small sizes and low charge ionic states, are most eligible to intercalate in the structural layers of V2O5. We have applied ab-initio density functio…
Phonon Softening and Pressure-Induced Phase Transitions in Quartz Structured Compound, FePO4
R. Mittal, R. P. Hermann, M. Angst +5
Nuclear resonant inelastic x-ray scattering on quartz structured 57FePO4 as a function of pressure, up to 8 GPa reveals hardening of the low-energy phonons under applied pressures…
Solid-like to Liquid-like Behavior of Cu Diffusion in Superionic Cu2X (X=S, Se): An Inelastic Neutron Scattering and Ab-Initio Molecular Dynamics Investigation
Sajan Kumar, M. K. Gupta, Prabhatasree Goel +5
Cu2Se and Cu2S are excellent model systems of superionic conductors with large diffusion coefficients that have been reported to exhibit different solid-liquid-like Cu-ion diffusio…
Phonons and Thermodynamics of LiMPO4 (M=Mn, Fe)
Prabhatasree Goel, M. K. Gupta, R. Mittal +5
Lithium transition metal phospho-olivines are useful electrode materials, owing to their stability, high safety, low cost and cyclability. We report phonon studies using neutron in…
New Insights into the Compressibility and High-Pressure Stability of Ni(CN)2 from Neutron Diffraction, Raman Spectroscopy and Inelastic Neutron Scattering
S. K. Mishra, R. Mittal, M. Zbiri +7
The layered structure of tetragonal Ni(CN)2, consisting of square-planar Ni(CN)4 units linked in the a-b plane, with no true periodicity along the c-axis, is expected to show aniso…
Pressure dependence of the low- temperature crystal structure and phase transition behaviour of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study
S. K. Mishra, R. Mittal, S. L. Chaplot +8
We report systematic investigation of high pressure crystal structures and structural phase transition upto 46 GPa in CaFeAsF and 40 GPa in SrFeAsF at 40 K using powder synchrotron…
Ab initio studies of phonon softening and high pressure phase transitions of alpha-quartz SiO2
N. Choudhury, S. L. Chaplot
Density functional perturbation theory calculations of alpha-quartz using extended norm conserving pseudopotentials have been used to study the elastic properties and phonon disper…
Lattice Dynamics and Thermal Expansion Behavior in Metal Cyanides, MCN (M=Cu, Ag, Au): Neutron Inelastic Scattering and First Principles Calculations
M. K. Gupta, Baltej Singh, R. Mittal +2
We report measurement of temperature dependence of phonon spectra in quasi one-dimensional metal cyanides MCN (M=Cu, Ag and Au). Ab initio lattice dynamics calculations have been p…
Effects of magnetic doping and temperature dependence on phonon dynamics in CaFe\_{1-x}Co\_{x}AsF compounds (x = 0, 0.06, 0.12)
R. Mittal, M. Zbiri, S. Rols +9
We report detailed measurements of composition as well as temperature dependence of the phonon density-of-states in a new series of FeAs compounds with composition CaFe1\_{1-x}Co\_…
Phonons, Phase Transitions and Thermal Expansion in LiAlO2: An ab-initio Density Functional Study
Baltej Singh, M. K. Gupta, R. Mittal +1
We have used ab-initio density functional theory technique to understand the phase transitions and structural changes in various high temperature/pressure phases of LiAlO2. The ele…
Negative Thermal Expansion Behaviour in MZrF6 (M=Ca, Mg, Sr): Ab-initio Lattice Dynamical Studies
M. K. Gupta, Baltej Singh, R. Mittal +1
The thermal expansion behavior of metal fluorides can be tuned by choosing appropriate metal cation. We present ab-initio lattice dynamical studies on the metal fluorides (CaZrF6,…
Investigation of phonon dynamics of perovskite multiferroic manganites: RMnO3 (R=Tb, Dy, Ho)
Renu Choithrani, Mala N. Rao, S. L. Chaplot +2
We have used a shell model to study the phonon dynamics of multiferroic manganites RMnO3 (R= Tb, Dy, Ho). The calculated phonon dynamical properties, crystal structure, Raman frequ…
Phonons, Nature of Bonding and Their Relation to Anomalous Thermal Expansion Behavior of M2O (M=Au, Ag, Cu)
M. K. Gupta, R. Mittal, S. L. Chaplot +1
We report a comparative study of the dynamics of Cu2O, Ag2O and Au2O (i.e. M2O with M = Au, Ag and Cu) using first principle calculations based on the density functional theory. He…
Phonons and Anomalous Thermal Expansion Behaviour of H2O and D2O ice Ih
M. K. Gupta, R. Mittal, Baltej Singh +4
In order to identify and quantitatively analyze the anharmonicity of phonons relevant to the anomalous thermal expansion in the Ih phase of ice, we performed neutron inelastic scat…
Investigating Anomalous Thermal Expansion of Copper Halides by Inelastic Neutron Scattering and Ab-inito Phonon Calculations
Abhijith M. Gopakumar, M. K. Gupta, R. Mittal +2
We investigate detailed lattice dynamics of copper halides CuX (X=Cl, Br, I) using neutron inelastic scattering measurements and ab-initio calculations aimed at a comparative study…
Phonon spectra in CaFe2As2 and Ca0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison with ab-initio and shell model calculations
R. Mittal, S. Rols, M. Zbiri +10
We report the pressure and temperature dependence of the phonon density-of-states in superconducting Ca0.6Na0.4Fe2As2 (Tc=21 K) and the parent compound CaFe2As2, using inelastic ne…
Lattice Dynamics and High Pressure Phase Stability of Zircon Structured Natural Silicates
Preyoshi P. Bose, R. Mittal, S. L. Chaplot
We report a lattice dynamics study of relative stability of various phases of natural silicates MSiO4 (M=Zr, Hf, Th, U) as a function of pressure (P) and temperature (T), which is…
Phonon dynamics in Sr0.6K0.4Fe2As2 and Ca0.6Na0.4Fe2As2
R. Mittal, Y. Su, S. Rols +6
We report inelastic neutron scattering measurements of the phonon density-of-states in superconducting Sr0.6K0.4Fe2As2 (Tc=30 K) and Ca0.6Na0.4Fe2As2 (Tc=18 K). Compared with the p…
Anomalous Phonons in CaFe2As2
R. Mittal, L. Pintschovius, D. Lamago +9
Extensive inelastic neutron scattering measurements of phonons on a single crystal of CaFe2As2 allowed us to establish a fairly complete picture of phonon dispersions in the main s…
Spin-Phonon Coupling and High Pressure Phase Transitions of RMnO3 (R= Ca and Pr): An Inelastic Neutron Scattering and First Principle Studies
S. K. Mishra, M. K. Gupta, R. Mittal +2
We report inelastic neutron scattering measurements over 7-1251 K in CaMnO3 covering various phase transitions, and over 6-150 K in PrMnO3 covering the magnetic transition. The exc…
Lattice dynamical calculations of infinite layer iron oxides SrFeO2 and CaFeO2
R. Mittal, S. L. Chaplot, Y. Su
We report extensive lattice dynamical calculations of the newly discovered infinite-layer iron oxides SrFeO2 and CaFeO2. For SrFeO2, the parameters of the interatomic potential hav…
Collective dynamics in crystalline polymorphs of ZnCl: potential modelling and inelastic neutron scattering study
A. Sen, Mala N. Rao, R Mittal +1
We report a phonon density of states measurement of -ZnCl using the coherent inelastic neutron scattering technique and a lattice dynamical calculation in four crystallin…
Evidence for existence of Functional Monoclinic Phase in Sodium Niobate based Solid Solution by Powder Neutron Diffraction
S. K. Mishra, Mrinal Jauhari, R. Mittal +3
We have carried out systematic temperature-dependent neutron diffraction measurements in conjunction with dielectric spectroscopy from 6 to 300 K for sodium niobate based compounds…
Phonons and Stability of Infinite-Layer Iron Oxides SrFeO2 and CaFeO2
M. K. Gupta, R. Mittal, S. L. Chaplot +2
We present detailed ab-initio lattice dynamical analysis of the Fe-O infinite-layer compounds CaFeO2 and SrFeO2 in various magnetic configurations. These indicate strong spin-phono…
Inelastic Neutron Scattering Studies of Phonon Spectra and Simulations in Tungstates, AWO4 (A = Ba, Sr, Ca and Pb)
Prabhatasree Goel, M. K. Gupta, R. Mittal +4
Lattice dynamics and high pressure phase transitions in AWO4 (A = Ba, Sr, Ca and Pb) have been investigated using inelastic neutron scattering experiments, ab-initio density functi…
Probing of Structural Phase Transitions in Barium Titanate Modified Sodium Niobate using Raman Scattering
Mrinal Jauhari, S. K. Mishra, R. Mittal +1
Raman Spectroscopic measurements are carried out to investigate the structural phase transitions as a function of composition in modified sodium niobate [(1-x) NaNbO3-xBaTiO3:NNBTx…
Negative Thermal Expansion in cubic ZrW2O8: Role of Phonons in Entire Brillouin Zone From ab-inito Calculations
M. K. Gupta, R. Mittal, S. L. Chaplot
We report ab-inito density functional theory calculation of phonons in cubic phase of ZrW2O8 in the entire Brillouin zone and identify specific anharmonic phonons that are responsi…
Pressure dependence of phonon modes across the tetragonal to collapsed tetragonal phase transition in CaFe2As2
R. Mittal, R. Heid, A. Bosak +14
The pressure dependence of a large number of phonon modes in CaFe2As2 with energies covering the full range of the phonon spectrum has been studied using inelastic x-ray and neutro…
Competing antiferroelectric and ferroelectric interactions in NaNbO3 : Neutron diffraction and theoretical studies
S. K. Mishra, N. Choudhury, S. L. Chaplot +2
Neutron diffraction studies using powder samples have been used to understand the complex sequence of low temperature phase transitions of NaNbO3 in the temperature range from 12 K…
Lithium Diffusion in Li2X(X=O, S and Se): Ab-initio Simulations and Neutron Inelastic Scattering Measurements
M. K. Gupta, Baltej Singh, Prabhatasree Goel +3
We have performed ab-initio lattice dynamics and molecular dynamics studies of Li2X (X=O, S and Se) to understand the ionic conduction in these compounds. The inelastic neutron sca…
Phonon Dispersion Relation, High-Pressure Phase Stability and Thermal Expansion in YVO4
R. Mittal, M. K. Gupta, Baltej Singh +3
The orthovanadates are useful as host matrices for immobilization of radioactive wastes. The thermodynamic stability of these materials is crucial for their applications in high pr…
High Temperature Phase Stability in Li0.12Na0.88NbO3: A Combined powder X-Ray and Neutron Diffraction Study
S. K. Mishra, P. S. R. Krishna, A. B. Shinde +4
Lithium doped sodium niobate is an ecofriendly piezoelectric material that exhibits a variety of structural phase transitions with composition and temperature. We have investigated…
Phonons and Anisotropic Thermal Expansion Behaviour of NiX (X = S, Se, Te)
Prabhatasree Goel, M. K. Gupta, S. K. Mishra +5
Metal Chalcogenides have been known for important technological applications and have attracted continuous interest in their structure, electronic, thermal and transport properties…
Suppression of Antiferroelectric State in NaNbO3 at High Pressure from In Situ Neutron Diffraction
S. K. Mishra, M. K. Gupta, R. Mittal +2
We report direct experimental evidence of antiferroelectric to paraelectric phase transition under pressure in NaNbO3 using neutron diffraction at room temperature. The paraelectri…
Phonons and Colossal Thermal Expansion Behavior of Ag3Co(CN)6 and Ag3Fe(CN)6
R Mittal, M. Zbiri, H. Schober +3
Recently colossal positive volume thermal expansion has been found in the framework compounds Ag3Co(CN)6 and Ag3Fe(CN)6. Phonon spectra have been measured using the inelastic neutr…
Phonon Dynamics and Inelastic Neutron Scattering of Sodium Niobate
S. K. Mishra, M. K. Gupta, R. Mittal +4
Sodium niobate (NaNbO3) exhibits most complex sequence of structural phase transitions in perovskite family and therefore provides as excellent model system for understanding the m…
Dynamic Disorder in Negative Thermal Expansion Compound Zn(CN)2
R. Mittal, S. Mitra, H. Schober +2
Dynamical disorder in negative thermal expansion compound Zn(CN)2 is investigated by quasielastic neutron scattering technique in the temperature range 170-320 K. Significant quasi…