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Herein we report the structure, magnetic and dielectric properties of Y2CoMnO6 (YCMO) and Y2NiMnO6 (YNMO) prepared under various conditions. On annealing in inert atmosphere, YCMO sample shows a partial decomposition while YNMO remains unaffected. Both YCMO and YNMO samples show paramagnetic to ferromagnetic transition around 80 K, but only the magnetic properties of YCMO samples depend on the preparation conditions. YCMO samples show antiferromagnetic ground state in zero field and a metamagnetic transition at relatively low field (~2 T). Differences in the annealing environment do not destroy the initial antiparallel spin order in YCMO, but affect the critical fields of metamagnetic transition. The field-dependent magnetic properties indicated soft ferromagnetic nature of YNMO samples. The dielectric measurements show distinct frequency and temperature-dependent features in YCMO samples compared to YNMO samples. A large relative permittivity with e׳ of about 104 is observed in both O2 and air-annealed YCMO samples. Multiple dielectric relaxations are observed in all the annealed YCMO and YNMO samples.

A series of compositions with general stoichiometry Ca1−xZr1−xNd2xTi2O7 has been prepared by high-temperature solid-state reaction of component oxides and characterized by powder X-ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi2O7–Nd2Ti2O7 system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd2Ti2O7 structure types are observed in this system. The 4M-polytype of zirconolite structure is stabilized by substitution of Nd3+ ion. The addition of Nd3+ ions form a cubic perovskite structure-type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure-type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca2+ and Zr4+ are incorporated into the perovskite-type Nd2Ti2O7 structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd3+-rich compositions.

Orthorhombic InVO4 was prepared by solid-state reaction method and characterized by powder X-ray diffraction and scanning electron microscopy. The frequency-dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature.

Lanthanum gallate (LaGaO3) is known to undergo orthorhombic to rhombohedral first order phase transition at 150 °C. In this article we have shown that by introducing 2% La deficiency in the system, coexistence of above two phases can be obtained at lower temperature and a complete phase transition occurs at 200 °C. The evolution of structural parameters of the system with temperature is reported from X-ray diffraction measurements and Rietveld analysis of the diffraction patterns. The change in local octahedral distortion due to 2% La deficiency is revealed through the shift in the phonon modes of GaO6 octahedra, in both orthorhombic and rhombohedral phase.

Several materials properties of rutile $TiO_2$ (together with its other polymorphs) have been widely investigated in view of both fundamental and practical interest. It is a wide band gap $(E_g=3.05 eV)$ semiconductor that finds application, among others, as a photocatalyst for splitting water[1] into $H_2$ and $O_2$ and remediation of organic pollutants.[2] Among the lesswell-known properties of $TiO_2$ is its abnormally large static dielectric permittivity that shows strong frequency dependence as well as the associated soft $A_{2u}$ mode that decreases with decreasing temperature.[3,4] The latter, however, never becomes completely soft, even at 0 K. Accordingly, rutile is classified as an incipient ferroelectric.[4] The soft $A_{2u}$ mode involves displacement of the positively charged $Ti^{4+}$ against negatively charged $O^{2-}$ that manifests in a large static dielectric permittivity (165–250) along the tetragonal c axis. The special dielectric behavior of $TiO_2$ is different from that of the other rutile oxides such as $GeO_2$ and $SnO_2$, clearly indicating the role of $d^0$ electronic configuration of $Ti^{4+}$ on the dielectric properties. It is known that transition metal oxides with $d^0$ electronic configuration undergo a second-order Jahn–Teller (SOJT) distortion of the $MO_6$ (M = metal) octahedra arising from a mixing of empty $d_0$ states of the transition metal with the O 2p states.[5] The distortion seems to be at the heart of several of the interesting dielectric/ferroelectric properties of $d^0$ transition-metal-containing perovskite oxides[6] such as $BaTiO_3$, $PbTiO_3$, $PbZr_{1-x}Ti_xO_3$, $Pb_3MgNb_2O_9$, and so on.

In this article, we report the structural phase transitions in Bi4V2O11 as observed from temperature-dependent Raman scattering and X-ray diffraction measurements. Four different types of highly disordered coordination polyhedra around the vanadium atoms with large dispersion of V–O bond lengths are observed in Bi4V2O11 at ambient temperature. The observed V–O bond lengths could be grouped into two categories, viz. shorter 1.7 A. The Raman modes of Bi4V2O11 could be assigned to vibration of these bonds and V–O–V linkages. We could correlate the difference in degree of anharmonicity of the phonon modes with temperature to differences in V–O bond strength. The local structure of vanadium–oxygen network in Bi4V1.8Cu0.2O10.7 was also obtained by similar studies. The effect of highly disordered anion sublattice in the doped compound is reflected in the broadening of the Raman modes.