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Valence stability of aliovalent ions is mostly correlated with lattice site potential in ionic crystals. Madelung electrostatic potential is obtained by adding all the lattice site potentials for all the ions present in a crystal structure. Therefore, valence stability and the stability of a crystal structure can be better understood with consideration of both the lattice site potential and Madelung electrostatic potential. This was first demonstrated more than four decades ago by one of the present authors. We revisit this situation by using re-calculated lattice site potential and Madelung electrostatic potential for perovskite structure type ABO

A multifunctional tandem cell has been fashioned by (i) replacing the conventional counter electrode in a n-type titanium dioxide-based quantum dot sensitized solar cell (QDSC) with a QD-sensitized p-type nickel oxide photocathode to harness maximum power-conversion efficiency, and (ii) by coating an electrochromic molybdenum oxide overlayer at the photoanode. Light harvesting In2S3 nano-flakes were deposited onto a mesoporous NiO semiconductor scaffold. On pairing with the n-QDSC, substantial gains in the photovoltaic performance were achieved owing to greater spectral utilization across the visible region. Improvements to the photoanode architecture were developed by embedding plasmonic Au NPs in the CdS QD-sensitized TiO2 layer to augment the light absorption via plasmonic and scattering effects which translated to higher photocurrent densities. A thin film of MoO3 was applied to the photoanode, which provided an electrochromic response upon illumination, due to the concurrent insertion of an electron and a cation in the MoO3 matrix. The power conversion efficiency (PCE) achieved was 6.01% for the n-QDSC half-cell (TiO2/CdS/Au/MoO3-nS2−/Sn2−-C-fabric) and 0.047% for the p-QDSC half-cell (NiO/In2S3-nS2−/Sn2−-C-fabric). A stellar PCE value of 7.99% was attained when the two half-cells were co-assembled in a tandem device, in spite of the disparity in performance between the photoanode and photocathode. The maximum transmission modulation for the tandem device under 1 sun irradiance was 34% and the photocoloration efficiency was 16.4 cm2 min−1 W−1 at 550 nm. The results highlight the potential opportunities for combining energy conversion and light management in photovoltaics based on nanotechnology.

The pyrochlore solid solution (Na0.33Ce0.67)(2)-(Ir1-xRux)(2)O-7 (0

Crystalline CrOCl3 contains [Cl2OCr(?-Cl)2CrOCl2] molecules with two square pyramidal CrOCl4 units sharing a common edge and with the Cr–O arranged anti, a new structure type for transition metal MOX3 compounds. Crystals are monoclinic with space group P21/c, Z = 4, with a = 5.735(5), b = 13.738(7), c = 11.318(4) A, ? = 90°, ? = 98.346(6)°, ? = 90°. Its IR and UV/Vis spectra are reported and compared with those of the C3v monomer found in the gas phase. Structures are also reported for M2[CrOCl5] (M = Cs or Rb) and show a pseudo-octahedral anion. Cs2[CrOCl5] adopts a K2PtCl6-type structure with [CrOCl5]2– ions randomly orientated, but Rb2[CrOCl5] is orthorhombic with space group Pnma with a = 13.6471(7), b = 9.9175(5), and c = 6.9562(4) A. Rietveld refinement of the data on the rubidium salt gave Cr–O = 1.628(1), Cr–CltransO = 2.652(7), Cr–CltransCl = 2.239(8)–2.342(3) A. Corresponding CrV oxide bromide species do not form

The hydrothermal synthesis of four bismuth titanate materials from common bismuth and titanium precursors under hydrothermal conditions is described. Reaction of NaBiO3·2H2O and anatase TiO2 in concentrated NaOH solution at 240 °C is shown to produce perovskite and sillenite phases Na0.5Bi0.5TiO3 and Bi12TiO20, depending on the ratio of metal precursors used. When KOH solution is used and a 1:1 ratio of the same precursors, a pyrochlore Bi1.43Ti2O6(OH)0.29(H2O)0.66 is formed. The use of a mixture of HNO3 and NaOH is shown to facilitate the formation of the Aurivillius-type bismuth titanate Bi4Ti3O12. The phases have been isolated separately as phase-pure powders and profile refinement of powder X-ray diffraction data allows comparisons with comparable materials reported in the literature. Analysis of Bi LIII-edge X-ray absorption near edge structure (XANES) spectra of the materials shows the oxidation state of bismuth is +3 in all of the hydrothermally derived products.

Hexagonal aluminum nitride nanocrystals have been prepared by the reaction of hexamethyldisilazane with Al cupferronate or AlCl3 under solvothermal conditions. The nanocrystals have been characterized by X-ray diffraction, transmission electron microscopy and spectroscopic methods. The nanocrystals have average diameters in the 10–20 nm range and are single-crystalline. A characteristic photoluminescence band is observed around 420 nm.

GaN nanocrystals (see Figure) of hexagonal structure and varying diameters have been prepared by the reaction of hexamethyldisilazane (HMDS) with gallium cupferron or GaCl 3 under solvothermal conditions. The nanocrystals show a size-dependent photoluminescence band in the 260-320 nm region, characteristic of quantum confinement.

We investigate the properties of GaN semiconducting nanoparticles as a potential candidate for photodetection in the solar-blind region. The photocurrent spectral response is studied spanning the range 1.6-5.5 eV. A significant fraction of the response is in the range 4-5.5 eV. The results are compared to other optical properties and the origins of the features observed in the spectra are speculated upon.

GaMnN films with 1–3% Mn deposited on Si(100) and Al 2 O 3 (0001) substrates, by the technique of nebulized spray pyrolysis by employing acetylacetonate precursors, have been characterized by X-ray diffraction, photoluminescence spectra and other techniques. The films are ferromagnetic and show magnetic hysteresis. The ferromagnetic T C increases with the Mn content, with the 3% Mn film showing a T C of ∼250 K. Anomalous Hall effect is observed below T C where the films exhibit a small negative magnetoresistance.

Microstructural features and oxidation states in multiferroic Lu2Fe2.1Mn0.9O7 have been investigated by neutron diffraction,transmission electron microscopy(TEM), and x-rayabsorption near edge spectroscopy. Our experimental results demonstrate the disordered distribution of Mn atoms in the FeO double (W) layers, indicating that structural modulations originate from the charge disproportionation, which is evidenced by the mixed-valence states of Fe ions.TEM measurements clearly reveal Mn doping induced chemical inhomogeneity and local distortions which are associated with the charge disproportionation in the W layers. In addition, the polarization is discussed in association with the lattice distortions and charge disproportionation.

3% and 5% Mn-doped GaN nanocrystals of different sizes, with the average diameters in the range of 4–18nm, have been prepared by two independent routes under solvothermal conditions starting with two different precursors. The reaction temperature was around 350°C in all the preparations. The nanocrystals so prepared exhibit ferromagnetism with magnetization (M) and Curie temperature (TC) values increasing with percent of Mn and particle size. The observation of ferromagnetism in Mn-doped GaN nanocrystals prepared at relatively low temperatures is of significance in understanding this potential in spintronics materials.

In an effort to find a simple and common single-source precursor route for the group 13 metal nitride semiconductor nanostructures, the complexes formed by the trichlorides of Al, Ga and In with urea have been investigated. The complexes, characterized by X-ray crystallography and other techniques, yield the nitrides on thermal decomposition. Single crystalline nanowires of AlN, GaN and InN have been deposited on Si substrates covered with Au islands by using the complexes as precursors. The urea complexes yield single crystalline nanocrystals under solvothermal conditions. The successful synthesis of the nanowires and nanocrystals of these three important nitrides by a simple single-precursor route is noteworthy and the method may indeed be useful in practice.