Structure cristalline de l'orthophosphate monoacide de cuivre monohydrate CuHPO4,H2O

Monophosphate hydrogen copper monohydrate : CuHPO₄,H₂O is monoclinic, space group $\text{P}\text{2}{}_1\text{a}$. The unit cell parameters are : a = 8.63(6), b = 6.35(3), $\text{c}\text{= 6.82(5)}\text{A}\text{?}$, β = 94.14(6°) and Z = 4. The crystal structure has been determined with 1249 independent reflexions and refined to a final R value of 2.9%. The crystal is built up of PO₄ tetrahedron and CuO₆ octahedron deformed by Jahn-Teller effect which are linked to form a three dimensional network.Based on the inter-ionic distances between Cu^II and O^2? in the recently determined structures of monoarsenates or phosphates, we give a value for the effective ionic radius of copper II.     

Ionic conductivity of substituted Li2SO4 phases

Lithium ion conductivity of Li₂SO₄-Y₂(SO₄)₃, Li₂SO₄-La₂(SO₄)₃ and Li₂SO₄-Li₃PO₄ systems has been measured as a function of composition and temperature using AC complex impedance methods. Substitution of the trivalent cations results in a small enhancement of the ionic conductivity within the limit of solid solution formation. Considerable increase of the conductivity results by substitution of PO₄^3? for SO₄^2?. The maximum conductivity observed is $\text{1.1×10}{}^{\mathrm{?3}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300°C for the composition Li_2.2S_0.8P_0.2O₄ with E_a = 0.8 eV. These results are discussed in terms of the structural properties.     

Nouveaux conducteurs ioniques caracterises par une structure a tunnels entrecroises

The ionic conductivity of pyrochlores A_1+α(Ta_1+αW_1?α)O₆ was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and $\text{5 10}{}^{\mathrm{?8}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 5.5 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{500}\text{K}\text{≤ 10}{}^{\mathrm{?5}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T1_12+x(M_30+xW_3?x)O₉₀, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A₂M₇O₁₈ structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; $\text{3.6 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 1.4 10}{}^{\mathrm{?6}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; $\text{10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}\text{≤}{}^{\mathrm{\sigma }}\text{25°}\text{C}\text{≤ 3.8 10}{}^{\mathrm{?7}}\text{(Θ}\text{cm}\text{)}{}^{\mathrm{?1}}$). The evolution ofionic conduction properties of all these compounds is discussed.     

Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.     

Etude des proprietes structurales et electrioues d'un nouveau conducteur anionique: PbSnF4

Three allotropic varieties of PbSnF₄ - α, β and γ - have been detected by DTA and X-ray diffraction. The α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively. The high temperature form γ - PbSnF₄ is cubic and of fluorite type. The structures of the tetragonal β - PbSnF₄ and the orthorhombic α - PbSnF₄ forms are derived from the same structural type. PbSnF₄ has a high anionic conductivity ($\text{σ200°C ? 10}{}^{\mathrm{?1}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$). The temperature dependence of the conductivity indicates the existence of a break in the activation energy at 90°C.     

Crystal structure and cation transport properties of the ortho - diphosphates Na7(MP2O7)4PO4 (M = Al,Cr, Fe)

The isotypic ortho-diphosphates Na₇(MP₂O₇)₄PO₄ (M = Al, Cr, Fe) have been synthesized. They are tetragonal, space group P4&#x0304;2₁c. The structure of the iron member has been solved and refined to a final R = 0.037 for 577 independent reflections. It consists of (FeP₂O₇)₄PO₄ units interconnected so as to form a 3D framework into which the sodium ions are inserted. The units are made of a PO₄ tetrahedron linked to four FeO₆ octahedra; each octahedron is connected to a P₂O₇ group by two oxygens. Ion exchange experiments and conductivity measurements give evidence of some mobility of the sodium ions at high temperature. However, the σ-values ($\text{～ 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 300°C) are relatively low. The narrowness of the windows between the sodium sites as well as the presence of an oxygen atom linked to only one polyhedron of the framework are unfavourable features to fast cation transport.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.     

Polycrystalline hydronium ββ″alumina: A ceramic fast proton conductor

Polycrystalline hydronium $\text{β}\text{β″}\text{-}\text{alumina}$ with f(β) of 0.16 to 0.25 has been fabricated with an electrical conductivity of $\text{～ 10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 22°C and an activation energy of 0.24 eV (T < 100°C) and 0.09 eV (T > 100°C). This is comparable with single crystal behaviour. Proton magnetic resonance is correlated with conductivity and the effects of disorder on the conduction plane of the β″-alumina structure are shown to be important.     

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd,Hg, Pb. Correlation entre conductivite et structure

The glass-forming regions in the AgPO₃ ? MI₂ systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of $\text{10}{}^{\mathrm{?2}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is obtained for a mole fraction of 0,19 in PbI₂ or in CdI₂, whereas a value of $\text{3×10}{}^{\mathrm{?5}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is found for a mole fraction of 0,5 in HgI₂. The conductivity results and Raman spectra are examined and compared with those of AgPO₃ ? AgI. An exchange between Ag⁺ and M²⁺ ions is proposed leading to AgI species in AgPO₃ ? CdI₂ and AgPO₃ ? PbI₂ glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.     

Growth,electrical and photoelectrical properties of Tl3SbS3single crystal

The growth of Tl₃SbS₃ single crystal is reported for the first time. 5×1×1 cm³ ingots are obtained by using vertical Bridgmann method with a 2°C/mm gradient and a 0.7 mm/h growth rate. Intrinsic conductivity and photoconductivity are investigated. The weak dark conductivity, $\text{～ 10}{}^{\mathrm{?10}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300° K, contrasts with a strong photosensitivity. The value of the fundamental band gap deduced from spectral dependence of the photocurrent is in rather good agreement with the value 1.61 eV obtained from temperature dependence of the dark conductivity. The Lux-Ampere characteristics can be described by I ∝ L ^α but changes in α with illumination intensity and temperature show that at least two different local centers are involved in the carrier recombination mechanism.     

Conductivite ionique dans les verres AgPO3-AgX (X = I.Br.Cl)

The glass-forming regions in the systems AgPO₃- AgX with X = I.Br.Cl were determined and the study of the electrical conductivity of glasses belonging to these systems was carried out. The glass-forming region and conductivity increase with increasing halogen ion size. The conductivity reaches maxima values of the order of 10^?2, 10^?3, $\text{10}{}^{\mathrm{?4}}\text{(Ω ·}\text{cm}\text{)}{}^{\mathrm{?1}}$ with AgI, AgBr, AgCl respectively. The study of the electrical conductivity shows that the conduction is essentially ionic in nature and due to silver ions movements only.     

L'auto-extinction de Nd3+ : Son mecanisme fondamental et un critere predictif simple pour les materiaux minilaser

Crystal field is demonstrated to play an important role in the self quenching process of neodymium ⁴F_3/2 level. It arises essentially from the compensation by the crystal field of the difference in energy gravity center differences for states F_3/2, ⁴I_15/2, ⁴I_9/2 of the Nd³⁺ free ion. Using a new parameter Nv derived from the usual B^k_q parameters as an ordering parameter, a limit to the easily available ground state splitting is given : $\text{Δ}\text{E}\text{(}{}^4\text{I}{}_{\mathrm{9/2}}\text{) < 470}\text{cm}{}^{\mathrm{?1}}$. This is equivalent to Nv < 1800 cm^?1. In this instance melting or decomposition temperature is also considered : t_m,d < 1200°C.     

Thermal expansion of corundum structure Rh2O3

The directional thermal expansion coefficients of the corundum structure form of Rh₂O₃ were determined from room temperature to 850°C by x-ray diffraction methods. Rh₂O₃ has a lower thermal expansion and is less anisotropic in thermal expansion than alumina. The directional thermal expansion coefficients of Rh₂O₃ expressed in second degree polynominal form are: $\text{“α}{}_{\mathrm{<mtext>a</mtext>}}\text{” = 5.350 ×10}{}^{\mathrm{?6}}\text{+ 1.281 ×10}{}^{\mathrm{?9}}\text{T}\text{? 1.133 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$ and $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Structure cristalline d'un phspho-tellurate de rubidium : Te(OH)6.Rb2HPO4.RbH2PO4

Te(OH)₆.Rb₂HPO₄.RbH₂PO₄ is monoclinic with_°: a = 12.26(1) b = 7.059(3) c = 8.225(3) A β = 90.32(5)° and Z = 2. The space group is $\text{P}\text{2}{}_1\text{a}$. Crystal structure has been solved by using 1093 independant reflexions with a final R value 0.051. As already observed in the first crystal structures of phospho-tellurates the main feature of this atomic arrangement is the coexistence of two different types of anions in the unit cell (PO₄ and Te(OH)₆ groups).     

Chromium-doped CdF2 crystals by ESR spectroscopy

Single crystals of Cr-doped CdF₂ in which only Cr²⁺ ions were present were obtained by heating CdF₂:CrF₃ samples in Cd vapors. The crystals produced were studied by ESR spectroscopy at X band at 4.2 ^oK. The spectrum obtained is described by the effective spin Hamiltonian:

g⁽²⁾_eff = 4g_zcosΘ, g⁽¹⁾_eff = 2g_zcosΘ, where i = 1 for the doublet of the spin S = 1, and i = 2 for the doublet of the spin S = 2; net effective spin $\text{S}\text{=}\text{1}\text{2}$; g_z=1.85±0.03; |Δ₍₂₎|=3.08±0.07 GHz; |Δ₍₁₎|=5.85±0.07 GHz; $\text{1}\text{6}\text{(Δ}{}^{\mathrm{o}}{}_{\mathrm{(2)}}\text{? Δ}{}^{\mathrm{o}}{}_{\mathrm{(1)}}\text{)=?11.01±0.02}\text{GHz}$.     

Ionic conductivity in low carnegieite compositions based on NaAlSiO4

Carnegieite compositions of the type Na_1+xAl_1+xSi_1?xO₄ with x = 0 to ～0.7 were prepared. Na ion conductivities, measured with Na and Au electrodes at ～10³ Hz, range from $\text{4×10}{}_{\mathrm{?5}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ for NaAlSiO₄ to $\text{5×10}{}^{\mathrm{?3}}\text{(Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300 C for Na_1.7Al_1.7Si_0.3O₄. Substitutions of Li, K, Ca, or Sr for Na lowered σ whereas substitution of Ti for Si raised σ. Na aluminum silicates with the nepheline structure had lower σ than carnegieite compositions.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

Crystal structure of KHSO4 · KH2PO4

KHSO₄ · KH₂PO₄ is monoclinic $\text{P}\text{2}{}_1\text{n}$ with Z = 2 and the following unit cell dimensions: a = 7.434(3); b = 7.341(3); $\text{c}\text{= 7.148(3)}\text{A}\text{?}$; β = 99.56(5)°.Crystal structure of this salt has been solved, using 1699 independent reflexions with a final R value: 0.034. PO₄ and SO₄ tetrahedra are randomly distributed in the arrangement with a resulting (P.S)-O mean distance of 1.508(3) Å.     

Nature de la fluorescence de l'europium divalent dans les fluorures

The levels of the ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ (4f⁷) and 4f⁶5d¹ states of europium (+II) have been determined from fluorescence spectra in a series of fluorides M_xB_yF_z (M = alkaline-earth element, B = Li, Be, Mg, Y, Si). As in BaY₂F₈, SrSiF₆ and BaSiF₆, the ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ level lies even at room temperature far below the 4f⁶5d¹ band, only the f → f emission is observed. The influence of the choice of the alkaline-earth and the B cations and of the coordination of europium on the relative positions of the energy levels is discussed.