A thermal dehydration study of WO3.2H2O

Abstract: Step-wise thermal dehydration of WO3 . 2H(2)O has been investigated and the various hydrated tungsten trioxide phases characterized. A cubic phase of tungsten trioxide with 0.36 moles of water is obtained by heating WO3 . 2H(2)O to 498 K

A study of cubic bismuth oxides of the type bi(26-X)m(X)O(40-delta) (m=ti, mn, fe, co, ni or pb) related to gamma-bi2O3

A structural investigation of cubic oxides (space group I23) of the formula Bi(26-x)M(x)O(40-delta) (M = Ti, Mn, Fe, Co, Ni and Pb) related to the Y-Bi2O3 phase has been carried out by the Rietveld profile analysis of high-resolution X-ray powder diffraction data in order to establish the cation distributions. Compositional dependence of the cation distribution has been examined in the case of Bi26-xCoxO40-delta (1 < x < 16). The study reveals that in Bi(26-X)M(X)O(40-delta) with M = Ti, Mn, Fe, Co or Pb, the M cations tend to occupy tetrahedral (2a) sites when x < 2 while the octahedral (24f) sites are shared by the excess Co or Ni cations with Bi atoms when x > 2. Also experimental magnetic moments of Mn, Co and Ni derivatives have been used to establish the valence state and distribution of these cations

A study of superionic CsHSO<SUB>4</SUB> and Cs<SUB>1&#8722;x</SUB>Li<SUB>x</SUB>HSO<SUB>4</SUB> by vibrational spectroscopy and X-ray diffraction

Infrared and Raman spectroscopic studies of CsHSO4 suggest the occurrence of the following phase transitions: IV&#x21C6;340K III&#x21C6;380 K II&#x21C6;417K I. While the ordered phase, IV, has a monoclinic structure, the high-temperature superionic phase, I, has a tetragonal structure involving the free rotation of HSO4&#8722;. Phase II is close to being orthorhombic with a small monoclinic distortion. The transition to the superionic phase, I, is accompanied by the appearance of broad, structureless bands in the infrared and Raman spectra, as well as changes in the O-H stretching region due to decrease in hydrogen bonding. Accompanying the III-II transition, we observe the disappearance of the O&#183;&#183;&#183;O stretching and &#948;(S-OH) bands and a decrease in the HSO4&#8722; libration frequency. Across the phase transitions, the separation between the v(S-O) and v(S-OH) bands shows stepwise changes. The high-temperature superionic phase essentially has sulfate-like species with a relatively short S-O bond, in contrast to the low-temperature phase, which has long and short S-O distances. Substitution of Cs by Li in CsHSO4 has an effect similar to that of increasing the temperature. The vibrational spectrum of Cs0.7Li0.3HSO4 corresponds to a state of disorder between those of phases II and I

An x-ray crystallographic study of superconducting bismuth-lead cuprates without superlattice modulation

A single crystal x-ray crystallographic study of superconducting bismuth cuprate of the composition $BiPbSr_2Y_{0.5}Ca_{0.5}Cu_2O_8$ without any superlattice modulation has been carried out. The cuprate has an orthorhombic symmetry with the space group Pnan. Rietveld profile analysis was carried out with high-resolution powder data for this composition along with $BiPbSr_2YCu_2O_8$. The structural parameters so obtained are discussed

Metal-Insulator Transitions in Anion-Excess LaMnO3+? Controlled by the Mn4+ Content

LaMnO3+? samples with Mn4+ content up to 50% have been prepared by different methods. The structure of LaMnO3+? changes from orthorhombic to cubic (via rhombohedral) with increase in the Mn4+ content. LaMnO3+? samples containing greater than 20% Mn4+ are ferromagnetic and show resistivity maxima at a temperature Tt which is close to the ferromagnetic Curie temperature. The resistivity maximum is due to the occurrence of a metal-insulator transition. In samples heated to the same temperature, the value of Tt increases with % Mn4+. For a given sample, Tt increases with the temperature of heat treatment due to the increase in particle size. The onset of ferromagnetism in LaMnO3+? accompanied by an insulator-metal transition is similar to that found in La1-xCaxMnO3 and La1-xSrxCoO3

A Study of Superionic CsHSO4CsHSO_4 and Cs1−xLixHSO4Cs_{1-x}Li_xHSO_4 by Vibrational Spectroscopy and X-Ray Diffraction

Infrared and Raman spectroscopic studies of CsHSO4 suggest the occurrence of the following phase transitions: $IV\rightleftharpoons_{340K}III\rightleftharpoons_{380K}II\rightleftharpoons_{417K}I$. While the ordered phase, IV, has a monoclinic structure, the high-temperature superionic phase, I, has a tetragonal structure involving the free rotation of $HSO_4^-$. Phase II is close to being orthorhombic with a small monoclinic distortion. The transition to the superionic phase, I, is accompanied by the appearance of broad, structureless bands in the infrared and Raman spectra, as well as changes in the $O-H$ stretching region due to decrease in hydrogen bonding. Accompanying the III-II transition, we observe the disappearance of the $O \cdots O$ stretching and $\delta(S-OH)$ bands and a decrease in the $HSO_4^-$ libration frequency. Across the phase transitions, the separation between the v(S-O) and v(S-OH) bands shows stepwise changes. The high-temperature superionic phase essentially has sulfate-like species with a relatively short S-O bond, in contrast to the low-temperature phase, which has long and short S-O distances. Substitution of Cs by Li in $CsHSO_4$ has an effect similar to that of increasing the temperature. The vibrational spectrum of $Cs_{0.7}Li_{0.3}HSO_4$ corresponds to a state of disorder between those of phases II and I

Location of rare-earth atoms in isomorphous series of complex oxides by employment of difference Fourier syntheses based on X-ray powder profile analysis: La<SUB>3</SUB>LnBaCu<SUB>5</SUB>O<SUB>13+&#948;</SUB> (Ln=Y, La, Nd or Gd) and LnBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7&#177;&#948;</SUB> (Ln=Y, Nd, Pr, Gd or Dy)

Analysis of the X-ray powder diffraction profiles of an isomorphous series of inorganic solids has been carried out for two series of complex oxides: La<SUB>3</SUB>LnBaCu<SUB>5</SUB>O<SUB>13+&#948;</SUB> (Ln=Y, Nd or Gd) and LnBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7+&#948;</SUB> (Ln=Y, Nd, Pr, Gd or Dy). In this method, profile and structure refinements of a reference compound are followed by a difference Fourier synthesis to locate the positional parameters of a substituent atom. A linear correlation exists between the Fourier peak height in the difference Fourier map and the atomic number of the substituent atom. By an analysis of relative peak height in the correlation plot, the extent of cation disorder, if any, can be determined

An investigation of insulating La<SUB>4</SUB>BaCu<SUB>5</SUB>O<SUB>12</SUB> obtained by the reduction of metallic La<SUB>4</SUB>BaCu<SUB>5</SUB>O<SUB>13.1</SUB>

The structure of insulating La4BaCu5O12 obtained by the reduction of metallic La4BaCu5O13.1 has been studied by using electron microscopy and high-resolution X-ray diffraction data. While La4BaCu5O13.1 (P4/m) has a tetragonal structure with the supercell ac&#8730;5 &#215; ac&#8730;5 &#215; ac , the reduced phase, La4BaCu5O12, is monoclinic (P2/m) with the supercell ac&#8730;5 &#215; ac&#215; ac&#8730;5. La4BaCu5O12 consists of CuO5 square pyramids and CuO4 square planar units, instead of CuO6 octahedra and CuO5 square pyramids as in La4BaCu5O13.1. Electron microscopic examination reveals the presence of twinning in some of the crystals of La4BaCu5O12

Deffect Structure of LAMNO3

LaMnO3 compositions possessing orthorhombic, rhombohedral and cubic structures and containing 12, 24 and 33% Mn4+ respectively have been investigated by X-ray diffraction, electron diffraction and high resolution electron microscopy. The study shows that the defect structure of LaMnO3 is best described in terms of the random distribution of La and Mn vacancies, rather than by anion excess. Density measurements confirm the cation vacancy model involving an equal number of La and Mn vacancies