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La2NiMnO6 (LNMO) was prepared by a combustion method followed by heating at high temperature. Subsequently, the preformed LNMO was annealed in air, oxygen, or N2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis. Structural studies by XRD and neutron diffraction revealed the coexistence of partially cation disordered monoclinic (31%) and rhombohedral (69%) phases in the sample annealed in air. However, the sample annealed in oxygen shows about 50:50% of monoclinic and rhombohedral phases. Relaxor-like behavior with relative permittivity of the order of 104 was observed in the sample annealed in air, while relative permittivity decreases to about 200 in samples annealed in oxygen atmosphere. The magnetic properties indicate a well-defined ferromagnetic phase in the oxygen-annealed sample compared to a feeble ferromagnetic signature in the air-annealed one. The dielectric and ferromagnetism of LNMO samples have been related to formation and annihilation of oxygen vacancies.

We have studied the electronic properties at ambient pressure and under high pressure of InVO 4 , InNbO 4 , and InTaO 4 powders, three candidate materials for hydrogen production by means of photocatalytic water splitting using solar energy. A combination of optical absorption and resistivity measurements and band structure calculations have allowed us to determine that these materials are wide band-gap semiconductors with a band-gap energy of 3.62(5), 3.63(5), and 3.79(5) eV for InVO 4 , InNbO 4 , and InTaO 4 , respectively. The last two compounds are indirect band-gap materials, and InVO 4 is a direct band-gap material. The pressure dependence of the band-gap energy and the electrical resistivity have been determined too. In the three compounds, the band gap opens under compression until reaching a critical pressure, where a phase transition occurs. The structural transition triggers a band-gap collapse larger than 1.2 eV in the three materials, being the abrupt decrease in the band-gap energy related to an increase in the pentavalent cation coordination number. The phase transitions also cause changes in the electrical resistivity, which can be correlated with changes induced by pressure in the band structure. An explanation to the reported results is provided based upon ab initio calculations. The conclusions attained are of significance for technological applications of the studied oxides.

La 2 NiMnO 6 (LNMO) was prepared by a combustion method followed by heating at high temperature. Subsequently, the preformed LNMO was annealed in air, oxygen, or N 2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis. Structural studies by XRD and neutron diffraction revealed the coexistence of partially cation disordered monoclinic (31%) and rhombohedral (69%) phases in the sample annealed in air. However, the sample annealed in oxygen shows about 50:50% of monoclinic and rhombohedral phases. Relaxor-like behavior with relative permittivity of the order of 10 4 was observed in the sample annealed in air, while relative permittivity decreases to about 200 in samples annealed in oxygen atmosphere. The magnetic properties indicate a well-defined ferromagnetic phase in the oxygen-annealed sample compared to a feeble ferromagnetic signature in the air-annealed one. The dielectric and ferromagnetism of LNMO samples have been related to formation and annihilation of oxygen vacancies.

We have carried out neutron inelastic scattering measurement of the phonon density of states and lattice dynamic calculations for Y2O3 using ab-initio density functional perturbation theory and interatomic potential model. The calculations are found to be in good agreement with experimental data, indicating that the potential model can be used for the calculation of phase diagram of Y2O3. The model is then used for free energy calculation to understand the stability of various phases as a function of pressure and temperature.

Herein we report the results of high pressure diffraction studies of zircon type ThGeO4. ThGeO4 exhibits anisotropic compressibility with the average compressibility along a-axis (20.8 × 10−4/GPa) larger than that along c-axis (9.98 × 10−4/GPa). Fitting the pressure dependence unit cell volume to 3rd order Birch-Murnaghan equation of states, the zero pressure bulk modulus (Ko) and volume (Vo) of 166(5) GPa and 341.6(3) Å3, respectively have been obtained. Preliminary studies on temperature dependent neutron and x-ray diffraction studies on ThGeO4 revealed anisotropic expansion behaviour with larger expansion coefficient along c-axis compared to a-axis. No structural transition under temperature or pressure is observed in between ambient pressure to 10 GPa and in the temperature range of 25 to 1273K.

This chapter discusses the concept of multiferroic properties. Multiferroics are materials that have more than one ferroic polarization. Primarily the term “ferroic polarization” indicates spontaneous magnetization, spontaneous electric polarization, or spontaneous strain. Ferromagnetic and ferroelectric materials are characterized by hysteresis loops, which indicate the maximum magnetization/polarization with applied magnetic/electric fields, coercive magnetic/electric fields and remanent magnetization/polarization, etc. Depending on the mechanism of multiferroicity and its nature (phases and effect), multiferroic materials have been classified into different subgroups. Heterostructures and composites that show multiferroic behavior have two different origins, even though they exhibit coupled effects they can be treated as a separate class. A simple concept of magnetoelectric with ferroelectric and antiferromagnetic combination can exhibit exchange bias properties at a ferromagnetic interface. Electric polarization can control the orientation of the antiferromagnetic axis, and hence the ferromagnetic axis of the interface. The use of magnetoelectric properties in magnetic reading and writing and GMR heads is established commercial technology. The modern applications of magnetoelectric and multiferroelectric materials are essentially based on the idea of storing information through the electric and magnetic polarizations. This provides an additional degree of freedom over conventional ferroelectric or ferromagnetic materials in designing memory elements.