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This article provides an overview of the structural changes in bulk MoS2 flakes, post irradiation with 1.5 MeV proton micro beam. We have irradiated multilayer MoS2 flakes, with 1.5 MeV proton micro beam in the fluence range 15–2135 pC/µm2. The fluence has been varied at constant flux and energy in the quest of the optimized defect density. The impact of micro beam irradiation on the sample, has been assessed by Raman measurement. We have observed significant changes in the E 2g 1 and A1g Raman vibrational modes of MoS2 flakes post irradiation. The X-ray diffraction (XRD) studies demonstrate that there are systematic and significant structural changes in the MoS2 flakes, due to 1.5 MeV proton micro beam irradiation. The XRD findings reveals that the formation of double phase takes place, with 706 pC/µm2 of proton micro beam fluence at 1.5 MeV and beyond. Theoretical simulation to assess the defect density have been performed using stopping range of ions in matter software. [ABSTRACT FROM AUTHOR]

We report here, temperature dependent Raman spectroscopic measurements on polycrystalline MnV2O4 over the temperature range of 10–300 K. The main aim of this study is to investigate the spin–phonon correlations across the magnetic and structural transition temperatures in this system. Temperature dependent magnetization measurements combined with the low temperature Raman study show the existence of structural changes in MnV2O4 across the two successive phase transitions. Anomalous changes in line shape parameters in some of the Raman modes are observed during temperature dependent Raman measurements, indicating the presence of spin–phonon coupling. A significantly high spin–phonon coupling strength of 5.9 cm−1 suggests alteration of spin dynamics across magnetic transition temperature, TM (57 K). [ABSTRACT FROM AUTHOR]

The underlying physics which explains the role of cationic and anionic defect dynamics in determining the catalytic activity and ionic conductivity of aliovalent ion-doped ceria is complex and not yet fully understood. To address this issue, we have investigated the structural evolution of LaxCe1-xO2–δ, where x =0.1, 0.2, 0.3, 0.4, and 0.5. Rietveld refinements of the X-ray diffraction patterns reveal that the crystal structure belongs to a disordered fluorite phase for all samples. We find a systematic increase in the lattice parameter along with a gradual decrease in oxygen site occupancy with the increase in La3+ doping concentration. In Raman spectra of doped compounds, other than well-known crystalline F2g and defect related modes, we observe the presence of an additional Raman mode. The Raman line-shape analysis indicates the non-resonant Fröhlich character of this mode. Temperature dependent Raman measurements demonstrate unique characteristics of this Raman peak. In addition, from the change in relative intensity ratio of the Raman modes related to different types of defect states, we show that vacancies cannot be considered as isolated defects beyond a critical doping level. We propose that the evolution of Raman intensities of defect related modes and Fröhlich mode with the doping level can be used as a marker to determine the role of electron-phonon coupling and anion vacancies in the catalytic activity of doped ceria. Furthermore, by studying the photocatalytic measurements for La3+ doped ceria compounds, we demonstrate that the anion vacancies do not always play a direct role in controlling functional properties. [ABSTRACT FROM AUTHOR]

We embarked on a study of Scandium (Sc) doped (onto Ga site) gallium ferrite (GaFeO3) and found remarkable magnetic properties. In both doped as well as parent compounds, there were three types of Fe3+ions (depending on the symmetry) with the structure conforming to space group Pna21 (Sp. Grp. No. 33) below room temperature down to 5 K. We also found that all Fe3+ions occupy octahedral sites, and carry high spin moment. For the higher Sc substituted sample (Ga1-xScxFeO3:x = 0.3), a canted magnetic ordered state is found. Spin-phonon coupling below Néel temperature was observed in doped compounds. Our results indicated that Sc doping in octahedral site modifies spin-phonon interactions of the parent compound. The spin-phonon coupling strength was estimated for the first time in these Sc substituted compounds. [ABSTRACT FROM AUTHOR]

In this paper, we report the X‐ray diffraction studies over the temperature range of 300–900 K and subsequent Rietveld refinement of the diffraction patterns shows that there is no evidence of any structural phase transition in YCrO3 (YCO) across the paraelectric to ferroelectric phase transitions (TC~ 460 K), and the material retains the orthorhombic structure with Pnma space group. However, a detailed analysis reveals local distortions in the CrO6 octahedra. To probe the local structural distortion, we have carried out temperature‐dependent, unpolarized Raman measurements, from 300 to 600 K. YCrO3 shows a strong anomalous deviation in both phonon wavenumbers and line widths around TC. YCrO3 is reported to possess as an incipient ferroelectric material to show that there are two competing phenomenon—onset of ferroelectricity due to rotation of CrO6 octahedra and displacement of Y atom leading to suppression of ferroelectricity. This competition reveals that although the octahedral rotations favor a lower symmetry state, the Y atom displacement opposes it leaving YCO to exhibit only an incipient ferroelectric state. These results while being in agreement with the earlier theoretical predictions can also help suggest a pathway to a more stable ferroelectric state in these oxides by using a larger cationic substitution at the Y site. [ABSTRACT FROM AUTHOR]

In this article, we report negative thermal expansion and spin frustration in hexagonal GdInO3. Rietveld refinements of the x-ray diffraction patterns reveal that the negative thermal expansion in the temperature range of 50-100 K stems from the triangular lattice of Gd3+ ions. The downward deviation of the low-temperature inverse susceptibility (χ-1) versus T plot from the Curie-Weiss law and the large value of the ratio, 0CW|/TN>28, where θCW and TN are respectively Curie-Weiss and Neel temperature, indicate a strong spin frustration, which inhibits long-range magnetic ordering down to 1.8 K. Magnetostriction measurements clearly demonstrate a spin-lattice coupling in the system. Low-temperature anomalous phonon softening, as obtained from temperature-dependent Raman measurements, also reveals the same. Our experimental observations are supported by first-principles density functional theory calculations of the electronic and phonon dispersion in GdInO3. The calculations suggest that the GdInO3 lattice is highly frustrated at low temperature. Further, the calculated normal mode frequencies of the Gd-related G point phonon modes reveal significant magnetoelastic coupling in this system. The competitive role of magnetic interaction energy and thermal stabilization energy in determining the change in interatomic distances is the possible origin for the negative thermal expansion in GdInO3 over a limited range of temperature. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of the Y 1-x Tb x MnO 3 (0.1  ⩽  x  ⩽  0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x  =  0.1 sample magnetic moments of the Tb 3+ ionic as well as Mn 3+ ionic were ordered. At 5 K for the x  =  0.2 sample only the Mn 3+ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z  =  0 plane and three on the z  =  0.5 plane (where z corresponds to  +c axis).The Mn 3+ ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ B , and 2.90(3) µ B for the x  =  0.1 and the x  =  0.2 samples. The Tb 3+ ionic moments had a magnitude of 1.36(4) µ B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x  =  0.1 sample. The low moment in comparison with Mn 3+ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO 3 and also in another rare earth manganite viz HoMnO 3 . The x  =  0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y 1-x Tb x MnO 3 in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm -1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x  =  0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x  =  0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.