Phase equilibria in the system Nd2O3|P2O5|H2O at 500°C under 100 MPa and synthesis of NdP5O14 crystals

Phase equilibria in the system Nd₂O₃|P₂O₅|H₂O was studied under a hydrothermal condition at 500°C under 100 MPa by a quenching technique using encapsuled samples. Equilibria among Nd phosphates; NdP₅O₁₄, NdP₃O₉ and NdPO₄, and liquid phase could be attained within 24 h. The stability fields for liquid (L), NdP₅O₁₄+L, NdP₅O₁₄+NdP₃O₉+L, NdP₃O₉+L, NdP₃O₉+NdPO₄+L, NdPO₄+L and NdPO₄+Nd(OH)₃+H₂O have been determined. The composition of the liquid phase with which NdP₅O₁₄ and NdP₃O₉ or NdP₃O₉ and NdPO₄ could coexist was 3% Nd₂O₃-80% P₂O₅-17% H₂O or 4% Nd₂O₃-73% P₂O₅-23% H₂O respectively, at 500°C under 100 MPa. A phase diagram was constructed under this condition. Crystal growth of NdP₅O₁₄ were tried under the equilibrium condition. Diamond-shaped crystals 0.3 mm in size were grown at 500°C for 4 days under 100 MPa. Crystals tended to show aggregation and surface roughness at lower growth temperatures. The crystals with polyhedral shape and maximum 0.5 mm in size were grown at 650°C.     

The vibrational spectra of the intermediate compounds in the system Y2O3P2O5 and Gd2O3P2O5

The Infrared- and Raman-spectra of the intermediate compounds were studied for clues to their structural behavior as related to luminescence response. It was found that the degree of polymerization of PO₄ polyhedra increases in the phosphate-rich region and perhaps in the RE-oxide-rich region as well which was evident from the shift of stretching bands towards the higher energy side. Except in orthophosphates, the PO₄ polyhedra occupy more than one non-equivalent lattice site in all the phosphates.     

Studies on the system V3O5 /1b Ti3O5

The system (V_1?xTi_x)₃O₅ has been studied by means of X-ray powder photography, DTA and magnetic susceptibility measurements. A continuous series of solid solutions has been found for samples prepared at 1175 K, while samples prepared at 1275 K showed the solid solubility in the V₃O₅ end phase to be limited by $\text{x}\text{< 0.7}$ DTA studies have shown that the peak associated with the V₃O₅(low) /1b V₃O₅(high) transition disappears at $\text{x}\text{= 0.024}$. The DTA studies have also confirmed the existence of a phase transition in γ-Ti₃O₅ ($\text{x}\text{= 1}$) at 227 K.     

NdxLa1−xP5O14 single crystal fibers

Crystalline fibers of Nd_xLa_1?xP₅O₁₄, typically 10μm × 10μm in diameter and 1–2 mm long are grown from phosphoric acid solution. Growth in fiber form is accomplished by controlling the water content of the atmosphere above the crucible within the range of 23–293 grams/m³. The optical quality is good and a cw fiber laser has been constructed. Details of the crystal growth procedure are given.     

Subsolidus phase equilibria and the Li5Nd4FeO10 phase in the Li2O-Nd2O3-Fe2O3 system

A survey of the subsolidus phase equilibria in the system Li₂O-Nd₂O₃-Fe₂O₃ was made at subsolidus temperatures in the range 1000-1050 °C. A ternary phase was identified. The phase is centered on Li₅Nd₄FeO₁₀, with a cubic lattice a = 11.9494 Å. The compound melts incongruently at 1105 °C. The magnetic susceptibility was measured in the temperature range 4-300 K. The compound is paramagnetic in the temperature range 150-300 K and follows the Curie-Weiss law. At about T_N = 10 K, a long-range magnetic ordering is observed.     

Hydrogen insertion compounds of V6O13 and V2O5

Hydrogen insertion compounds H_xV₆O₁₃ (0<x?7.3) have been synthesised and characterised. Unit-cell dimensions, determined from powder X-ray analysis, indicate that the hydrogen-insertion reaction proceeds topotactically. In addition, a low-hydrogen-content phase of H_xV₂O₅ of similar structure to V₂O₅ has been prepared.     

Synthesis and selected properties of CrSbVO6 and phase relations in the V2O5–Cr2O3–α-Sb2O4 system in the solid state

Phase relations in the ternary oxide system V₂O₅–Cr₂O₃–α-Sb₂O₄ in the solid state in the atmosphere of air have been investigated by using the XRD, DTA/TG and IRS methods. Obtained results have shown that in the system the compound CrSbVO₆ is formed. This compound has been obtained both from oxides and from a mixture comprising CrSbO₄, CrVO₄ and SbVO₅ as well as from mixtures: CrSbO₄/V₂O₅, CrVO₄/α-Sb₂O₄ and SbVO₅/Cr₂O₃. A Solid product of incongruent melting of CrSbVO₆ at ∼1300°C is Cr₂O₃. CrSbVO₆ crystallizes in the tetragonal system and its calculated unit cell parameters amount to: a = b = 0.45719(12) nm, c = 0.30282(8) nm, Z = 2. The obtained results have allowed us also to divide the investigated system V₂O₅–Cr₂O₃–α-Sb₂O₄ into seven subsidiary subsystems and to determine temperatures and components concentration range in which CrSbVO₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

The possibility of intercalating alkali metals in a glass of the system V2O5 - P2O5

A semi-conducting phosphovanadate glass was tested as a possible material for positive electrode in solid state batteries.O.c. voltage with alkali metal (3.6 V/Li and 3.4 V/Na) is higher than for crystallized vanadium oxides and chemical intercalation of sodium or lithium is obtained using halogenated salts dissolved in organic solvents.     

The crystal structure of Ni5TiB2O10

The crystal structure of Ni₅TiB₂O₁₀ was determined by single crystal X-ray analysis. The compound has the same structure as the mineral ludwigite. The orthorhombic celldimensions and space group are $\text{a}\text{=9.206(7)}\text{A}\text{?}$, $\text{b}\text{=12.224(9)}\text{A}\text{?}$, $\text{c}\text{=2.994(2)}\text{A}\text{?}$, Pbam z=2. Ti and Ni are disordered on one equipoint.     

Magnetic anisotropy of V3O5

The magnetic anisotropy of V₃O₅ was investigated by magneto-torque measurements in the temperature range from 4.2 to 300 K. It has been confirmed that the Néel temperature is about 75 K and that two of the three principal axes vary with temperature in both the paramagnetic and antiferromagnetic states. The results are explained on a simplified four-sublattice model.     

The electrochemical behaviour of Co3O4 and CoO cathodes in high-temperature cells

Preliminary investigations of the electrochemical behaviour of $\text{LiA}\text{l}\text{LiC}\text{l}$, $\text{KC}\text{l}\text{Co}{}_3\text{O}{}_4$ and $\text{LiA}\text{l}\text{LiC}\text{l}$, $\text{KC}\text{l}\text{CoO}$ cells are reported. At an operating temperature of 420°C, maximum discharge capacities of up to 546 mA-h per gram of cobalt oxide were recorded during the early charge/discharge cycles. Cell performance deteriorated with further cycling due to (a) an instability of the cobalt oxides in the electrolyte, and (b) dispersion of the discharge product Li₂O into the electrolyte. During discharge, Co₃O₄ was reduced via CoO to Co metal. If excess Li₂O was added to the cathodes, CoO was oxidized to Co₃O₄ on charging, and further oxidation of Co₃O₄ gave rise to an unstable compound with postulated formula Li_2xCo₂O_3+x for $\text{x}\text{≧ 0}$. CoO was the most stable cobalt-oxide phase in the molten LiCl, KCl electrolyte.     

Electrical conductivity in Ta2O5

The defect structure of undoped polycrystalline Ta₂O₅ was investigated by determining the temperature [850–1050°C] and oxygen partial pressure [10⁰–10^?19 atm.] dependence of the electrical conductivity. The data were found to be proportional to the $\text{～?}\text{1}\text{4}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range <10^?8 atm. and independent of the oxygen partial pressure for P_O2 > 10^?6 atm. The enthalpy of formation of doubly ionized oxygen vacancies plus two electrons is estimated to be 118.31 Kcal/mole [5.13 eV]. The observed conductivity data are explained on the basis of the presence of unknown acceptor impurities in the undoped samples.     

High-pressure phase transition in Ho2O3

High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho₂O₃) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm⁻¹ disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.     

Phase transition in V3O5

A phase transition at 420°K previously unreported, has been discovered in V₃O₅. The transition is characterized by an endothermic DTA peak on heating and an abrupt change in the electrical resistivity at the same temperature. Results from X-ray analysis of the V₃O₅ samples exhibiting the transition agree very well with the values reported by Andersson (1). Powder diffraction analysis of the high temperature phase indicates that there is a small change in the cell volume but the crystal apparently conserves its symmetry through the transition.     

Sol-gel法制备BaTiO_3、BaTi_2O_5和BaTi_4O_9粉末

采用Sol-gel法合成了BaTiO3、BaTi2O5和BaTi4O9粉末,利用XRD和SEM研究了它们的晶相和微观结构。在较低温度烧结得到的粉末都存在一定量的杂相,随着烧结温度的升高,杂相逐渐消失。在1000℃以上温度烧结,可以得到单相BaTiO3和BaTi2O5粉末,而单相BaTi4O9粉末则在1300℃以上温度烧结得到。随着n(Ba)/n(Ti)减小,所得单相的烧结温度逐渐升高。随着烧结温度的升高,BaTiO3、BaTi2O5和BaTi4O9粉末的晶粒逐渐长大。800℃以上温度烧结得到的四方BaTiO3钙钛矿相粉末主要由方形和圆形的晶粒组成;1100℃烧结得到的单斜BaTi2O5相粉末主要由近似菱形的晶粒组成;在1200℃烧结得到的正交BaTi4O9相粉末基本由长形的晶粒组成。     

Enhancement of Sinter Densification of SrO-BaO-Nb2O5-SiO2 Tungsten-Bronze Glass-Ceramics by Doping with P2O5

Densification behaviors of SrO—BaO—Nb₂0₅—SiO₂ based glass—ceramics prepared by conventional sintering were investigated with an emphasis on the influence of P₂O₅ content.Although P₂0₅ dopant did not modify the surface crystallization mechanism,it resulted in a decrease of the glass transition temperature,which facilitates the viscous glass flow necessary for sintering.However,premature crystallization of（Sr,Ba）Nb₂O₆ induced by addition of excess amount of P₂0₅ essentially retarded sintering due to the formation of closed pores in the matrix.The SrO-BaO-Nb₂0₅-Si0₂ glass with 1.0 mol%P₂0₅（SBN-1P） showed the best sinter densification,which was accomplished at about 850℃.     

Refractories based on 3Er2O3-Ta2O5

Refractory Er₂O₃-Ta₂O₅ compositions in the high Er₂O₃ region were prepared by coprecipitation as hydroxides, followed by calcination. Based on x-ray diffraction and wet chemical and electron microanalysis, the fluorite phase was found at 17.3–34.2 (±0.5) mole percent Ta₂O₅. This fluorite phase was stable to at least 2140 C in reducing atmospheres; although measurable vaporization occurred above 1975 C. Above 2100 C minor Ta reduction with preferential vaporization of Er and O was observed.     

Crystal structures of KBa2Nb5O15 and LaK2Nb5O15 with the TTB-type structure

Single crystals of two niobates, KBa₂Nb₅O₁₅ and LaK₂Nb₅O₁₅, were synthesized by high-temperature reaction and the crystal structures were determined by single crystal X-ray diffraction data. Although the space groups for these compounds were different (the non-centrosymmetrical space group P4bm (#100) for KBa₂Nb₅O₁₅ and the centrosymmetrical one P4/mbm (#127) for LaK₂Nb₅O₁₅), both compounds had the same tetragonal tungsten bronze-type (hereafter TTB-type) structure. The lattice parameters and R-factors of KBa₂Nb₅O₁₅ (LaK₂Nb₅O₁₅) were a = 12.533(2) (12.563(2)) and c = 4.0074(9) (3.9179(9)) Å, and R₁ = 0.040 (0.047) and wR₂=0.131 (0.120), respectively. From the crystal structural analysis, it was clarified that distribution of two large cations was different from each other in the way that K and Ba atoms in KBa₂Nb₅O₁₅ were distributed statistically at two crystallographic sites and K and La atoms in LaK₂Nb₅O₁₅ were ordered.     

Superstructures and phase transitions of Bi2O3

Polymorphs of bismuth sesquioxide were studied by TG-DTA and X-ray diffraction methods and by electron microscopy. Phase transitions of the polymorphs are influenced not only by the temperature before cooling and the cooling rate but also by the duration of melting. New commensurate and incommensurate superstructure phases, observed under the electron microscope, are described as the Naxa types, where N is various value between 2 and 2.48. Here a stands for the cell dimension of the δ form, the fluorite-type structure. The superstructures can be derived by a scheme for ordering oxygen vacancies in the defective fluorite-type structure.     

Etude thermochimique de la synthese en phase vapeur de Y3Fe5O12

Thermochemistry of oxidation and hydrolysis of YCl₃ and FeCl₂ have been studied. It has been shown that Y₃Fe₅O₁₂ cannot be formed by hydrolysis. Conditions of synthesis have been established in oxidation, particularly it is pointed out that excess of HCl or Cl₂ is not recommended for moderating reactions. It makes the synthesis difficult to control. Theoretical results are compared to experimental data.