Publications

Aliovalent anion substitution in metal oxides and other inorganic materials has a remarkable effect on the electronic structures of these materials as recently demonstrated in N‐ and F‐cosubstituted ZnO. We have examined ZnO where O is partially substituted with N and Cl and found significant changes in the bond lengths by single‐crystal X‐ray crystallography in the case of ZnO 0.6 N 0.2 Cl 0.2 . Moderate substitution of N and Cl brings the band gap of ZnO down to 1.93 eV and renders ZnO coloured. These materials are photocatalytically active for hydrogen production. Complete substitution of O by N and Cl results in Zn 2 NCl, a colourless insulator. First‐principles calculations have shown how the presence of a band originating from N‐2p states occupying the top of the valence band is responsible for the reduction in the band gap in ZnO. The calculations have also thrown light on the stability and electronic structures of the N‐ and Cl‐cosubstituted ZnO compounds.

We report ferroelectricity with fairly large spontaneous polarization (P ~ 0.2 - 0.8 \muC/cm2) below the Neel temperature of chromium (TNCr) in weakly ferromagnetic rare-earth orthochromites, RCrO3 (R=rare-earth) only when the rare-earth ion is magnetic. Intriguingly, the ferroelectricity in ErCrO3 (TC = 133 K) disappears at a spin-reorientation (Morin) transition (TSR ~ 22 K) below which the weak ferromagnetism associated with the Cr-sublattice also disappears, demonstrating the crucial role of weak ferromagnetism in inducing ferroelectricity. Further, the ferroelectric polarization (P) could be reversed by reversing the spontaneous magnetization (M) by changing the polarity of magnetic field, indicating a strong magnetoelectric effect. We suggest that the ferroelectricity occurs in RCrO3, due to the combined effect of poling field that breaks the symmetry and the exchange field on R-ion from Cr-sublattice stabilizes the polar state. We propose that a similar mechanism could work in the isostructural rare-earth orthoferrites, RFeO3 as well.

Electrical resistivity behavior of single crystals as well as polycrystalline pellets of rare earth manganates has been investigated below the charge-ordering temperatures to understand the mechanism of conduction. The resistivity of both the single- and polycrystalline samples of Gd0.5Ca0.5MnO3 and Nd0.5Ca0.5MnO3 obey the T −1/4 law, characteristic of variable range hopping. A similar dependence is found in the hole-doped Pr0.6Ca0.4MnO3 as well, but the data of the electron-doped Pr0.4Ca0.6MnO3 do not seem to obey any T −1/n law satisfactorily. AC conductivity measurements also reflect the unusual nature of the electron-doped composition.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

No abstract is provided for this article.

Ein Cadmiumoxalatgitter dient als Wirt für ausgedehnte Alkalimetallhalogenid-Strukturen mit unterschiedlichen Dimensionen. Das Bild zeigt beispielsweise, wie die Cl−-Ionen eines dreidimensionalen KCl-Gitter in einem Cd6O24-Cluster eingebaut sind.

151Eu and 57Fe Mössbauer spectra of EuCoO3 have been recorded in the 78–1200 K temperature range. The spectra along with magnetic susceptibility, X-ray diffraction and other measurements have been employed to understand the electronic and magnetic properties of EuCoO3. The studies are consistent with Goodenough's description of the electronic properties of LaCoO3.

Raman studies on powder samples of C60·TDAE are reported in the temperature range of 296 to 14 K. The strongest line Ag(2) shows a doublet at 1454 and 1463 cm−1 whose relative intensities are strongly temperature dependent. The relative intensities of the Hg(7) and Hg(8) modes at 296 K are much higher than those in pure C60 and these intensitites increase at low temperatures. The phonon softening and broadening are compared with the result on alkali-doped C60 and the theoretical calculations.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.