Renu Choithrani

Lattice dynamics of manganites RMnO3 (R =Sm, Eu or Gd): instabilities and coexistence of orthorhombic and hexagonal phases

The lattice dynamical and allied properties of the multiferroic manganites SmMnO3, EuMnO3 and GdMnO3 were investigated in this work by means of a shell model with transferable pairwise interionic interaction potential. This shell-model potential is able to reproduce the available crystal structure and phonon frequencies. A zone center imaginary Au mode is observed in these lattice dynamics calculations that indicates metastability of the perovskite phase. Comparison of the Gibbs free energies in the orthorhombic and hexagonal phases points to the possible coexistence of the two phases of these manganites under ambient conditions.

Thermodynamic properties of SmMnO3, Sm0.55Sr0.45MnO3 and Ca0.85Sm0.15MnO3

We have investigated thermodynamic properties of the perovskite Sm(Ca,Sr)MnO3 manganites, probably for the first time, using the rigid ion model (RIM) after modifying its framework to incorporate the van der Waals attraction and the short-range Hafemeister–Flygare type overlap repulsion operating between the first and second neighbour ions. We have found that the evaluated thermodynamic properties reproduce the corresponding experimental data well, implying that the modified RIM properly represents the elastic nature of these perovskite manganite systems. The results of the present investigation can be further improved by including the ferromagnetic spin wave contribution and Jahn–Teller distortion effect in the framework of the modified RIM.

Mechanoluminescence, thermoluminescence, photoluminescence studies on Ca3Y2Si3O12:RE3+ (RE3+ = Dy3+and Eu3+) phosphors

Dy(3+) and Eu(3+) activated Ca3Y2Si3O12 phosphors were synthesized by the solid-state synthesis method. The phosphors were characterized by X-ray diffraction (XRD), mechanoluminescence (ML), thermoluminescence (TL) and photoluminescence (PL) to determine structure and luminescence. For ML glow curves, only one peak was observed, as only one type of luminescence centre was formed during irradiation. The Ca3Y2Si3O12:Dy(3+) TL glow curve showed a single peak at 151.55 °C and the Ca3Y2Si3O12:Eu(3+) TL glow curve peaked at 323 °C with a small peak at 192 °C, indicating that two types of traps were activated. The trapping parameters for both the samples were calculated using Chens peak shape method. Dy(3+)-activated Ca3Y2Si3O12 showed emission at 482 and 574 nm when excited by a 351 nm excitation wavelength, whereas the Eu(3+)-activated Ca3 Y2Si3O12 phosphor PL emission spectra showed emission peaks at 613 nm, 591 nm, 580 nm when excited at 395 nm wavelength. When excited at 466 nm, prominent emission peaks were observed at their respective positions with very slight shifts.

Transport properties of (Ca1−xSrx)Mn0.95Sb0.05O3 perovskites

The transport properties as a function of composition and temperature of (Ca{sub 1−x}Srx)Mn{sub 0.95}Sb0.{sub 05}O{sub 3} perovskite compounds have been investigated for the first time using extended rigid ion model (ERIM). (Ca{sub 1−x}Srx)Mn{sub 0.95}Sb0.{sub 05}O{sub 3} (x = 0.0, 0.10, 0.15 and 0.17) exhibit a single phase with an orthorhombic perovskite structure (Pnma). Furthermore, to understand better the thermodynamical properties of the present system, ERIM is developed and applied to study the specific heat for these compounds over a wide range of temperature. The trends of variation of computed thermodynamical and transport properties have shown remarkable good agreement with corresponding experimental data.The transport properties as a function of composition and temperature of (Ca1−xSrx)Mn0.95Sb0.05O3 perovskite compounds have been investigated for the first time using extended rigid ion model (ERIM). (Ca1−xSrx)Mn0.95Sb0.05O3 (x = 0.0, 0.10, 0.15 and 0.17) exhibit a single phase with an orthorhombic perovskite structure (Pnma). Furthermore, to understand better the thermodynamical properties of the present system, ERIM is developed and applied to study the specific heat for these compounds over a wide range of temperature. The trends of variation of computed thermodynamical and transport properties have shown remarkable good agreement with corresponding experimental data.

Investigation of magnetic properties of Sm0.55Sr0.45MnO3

In this paper, we report the enhancement of metal – insulator transition temperature (TMI) induced by magnetic field confirms the MR phenomenon. The polycrystalline Sm0.55Sr0.45MnO3 were synthesized using solid state reaction route. The XRD patterns using Full Prof Rietveld analysis shows that the sample has single phase nature without any detectable impurity. The SEM micrograph carried to observe the grain morphology and four probe resistivity measurements using with superconducting magnet to investigate the electrical behaviour. The sharp value of temperature coefficient of resistance (TCR) of 11% is used for infrared bolometric sensors.

Effect of Ag substitution on the structural and magnetic properties of Sm0.55Sr0.45MnO3 (x = 0, 0.15) system

We report the structural and magnetic properties of Ag substituted Sm0.55Sr0.45MnO3 (x = 0, 0.15) synthesized via solid state reaction method. The XRD patterns using Full Prof Rietveld analysis shows that the samples have single phase nature without any detectable impurity. SEM results shows that the grain size increases upto sharper instant. The magnetic studies reveals Neil temperature (TN) and Curie Temperature (Tc) get decreased with the lowering of temperature. The hysteresis loss which is dominant in pure sample disappears in Ag doped one. This shows that Ag helps in achieving the homogeneity thereby decreasing the disorder.

Transport properties of Ag doped Pr0.67Sr1−xAgxMnO3

We have synthesized and investigated the effect of Ag doping at x = 0 and 0.10 in Pr0.67Sr1−xAgxMnO3 via solid state reaction route. The Rietveld refinement of XRD data shows that these compounds crystallize in an orthorhombic structure with Pnma space group. On increasing the Ag content to x = 0.10, a linear variation in unit cell volume and lattice parameters is observed. The temperature dependent zero-field and in-field resistivity has been measured between 5 K to 300 K. The samples show a systematic variation in metal to insulator transition temperature and a large magnetoresistance (MR) is also observed with maxima at TMI. The highest value of Temperature Coefficient of Resistance (TCR) % has been observed by us for the first time.

Structural, transport and elastic properties of LaTiO3

The thermophysical properties such as structural, transport and elastic properties of the orthorhombic perovskite-type titanate system, LaTiO3 have been explored in detail for the first time by applying extended rigid ion model (ERIM). LaTiO3 has been subject of recent interest because of the variety of attractive behaviors, including a metal-insulator transition, spin-charge-orbital ordering and high-temperature superconductivity. LaTiO3 has been suggested to have promising scientific and technological applications. The theoretically computed thermophysical properties of LaTiO3 compound are in good agreement with the available results.

Phonon Dynamics of Multiferroics: (Er, Tm) MnO3

The phonon dynamics of orthorhombic multiferroic perovskite RMnO3 (R = Er, Tm) using a shell model with pairwise interionic interaction potential has been investigated. The present work includes the computation of the structural parameters, phonon frequencies and the specific heat curves. The symmetry vectors obtained through detailed group‐theoretical analysis for Pnma space group at the zone center point were employed to classify the phonon frequencies obtained into their irreducible representations. The evaluated phonon dynamical properties are in good agreement with the available experimental data.

Thermo physical Properties of Multiferroic Rare Earth Manganite GdMnO3

We have investigated the thermophysical properties of multiferroic rare earth manganite GdMnO3 in the temperature range 15 K⩽T⩽300 K. We have applied interatomic potential to study the Specific heat (C) as a function of temperature. The calculated Specific heat values are closer to the available experimental data. At room temperature, the orthorhombic GdMnO3 phase is indicative of a strong Jahn‐Teller distortion. In addition, we have reported the cohesive energy (φ), molecular force constant (f), compressibility (β), Restrahalen frequency (ν0), Debye temperature (ΘD) and Groneisen parameter (γ) at temperature 15 K⩽T⩽300 K.