Low temperature heat capacity of Nd2Zr2O7 pyrochlore

Heat capacity of neodymium zirconate (Nd₂Zr₂O₇) with pyrochlore structure was measured by adiabatic calorimetry and the hybrid adiabatic relaxation method in the temperature range (0.45 to 400) K. Its excess component was obtained by comparison with the heat capacity of the lanthanum zirconate. A thermal anomaly was observed below T=7.2 K. From the heat capacity measurements, the thermodynamic functions of Nd₂Zr₂O₇ were determined.     

A Partial System LaPO4-Ca2P2O7-Ca(PO3)2-La(PO3)3

The system LaPO₄-Ca₂P₂O₇-Ca(PO₃)₂-La(PO₃)₃ was investigated by means of thermal and X-ray analyses. Three binary systems were found to occur in this region: LaPO₄-Ca(PO₃)₂,LaPO₄-Ca₄P₆O₁₉ and LaPO₄-CaLa(PO₃)₅. Their phase diagrams, and also that for the system LaPO₄-Ca₂P₂O₇- Ca(PO₃)₂-La(PO₃)₃, were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fe2P2O7(H2O)2

The compound diiron diphosphate dihydrate, Fe₂P₂O₇(H₂O)₂, was synthesized hydro­thermally and crystallizes in the monoclinic space group P2₁/n. The compound has a somewhat open framework made up of edge‐sharing iron(II) octahedra that form chains connected by five bridging diphosphates. The remaining octahedral site of each iron is occupied by coordinated water. The H atoms of the water molecules all point into a common channel.     

NaMn6(P2O7)2(P3O10) and KCd6(P2O7)2(P3O10)

The crystal structures of two new diphosphates, sodium hexamanganese bis­(diphosphate) triphosphate, NaMn₆(P₂O₇)₂(P₃O₁₀), and potassium hexacadmium bis­(diphosphate) triphosphate, KCd₆(P₂O₇)₂(P₃O₁₀), confirm the rigidity of the M₆(P₂O₇)₂(P₃O₁₀) matrix (M is Mn or Cd) and the relatively fixed dimensions of the tunnels extending in the a direction of the unit cell. The compounds are isomorphous; the P₂O₇^4? anion and the alkali metal cations lie on mirror planes. Bond‐valence analysis of the bonding details of the atoms found within the tunnels permits a prediction of the conductivity.     

The system Mg2P2O7−Na8Mg6(P2O7)5−NaPO3−Mg(PO3)2

Phase equilibria in the partial system Mg₂P₂O₇?Na₈Mg₆(P₂O₇)₅?NaPO₃?Mg(PO₃)₂ were examined by differential thermal analysis and powder X-ray diffraction. It was found that there are six sections in the composition range under investigation.     

The system YPO4-Mg3(PO4)2-Mg2P2O7

Phase equilibria in the systems YPO₄-Mg₃(PO₄)₂, YPO₄-Mg₂P₂O₇ and YPO₄-Mg₃(PO₄)₂-Mg₂P₂O₇ have been examined by thermal, X-ray and microscopic methods. Their phase diagrams have been provided.

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Zusammenfassung Mittels thermischen, röntgenografischen und mikroskopischen Methoden wurden die Phasengleichgewichte in den Systemen YPO₄-Mg₃(PO₄)₂, YPO₄-Mg₂ P₂O₇ und YPO₄-Mg₃(PO₄)₂-Mg₂P₂O₇ untersucht und deren Phasendiagramme ermittelt.

     

High-temperature heat capacity of zirconolite (CaZrTi2O7)

Enthalpy increment measurements in the range of (520 to 1570) K were carried out utilizing drop calorimetry on zirconolite (CaZrTi₂O₇). The high-temperature dependence of the heat capacity of zirconolite has been determined from the simultaneous analysis of our enthalpy increment measurements and published low-temperature heat capacity data.     

Cyclic carbonate based-electrolytes enhancing the electrochemical performance of Na4Fe3(PO4)2(P2O7) cathodes for sodium-ion batteries

Binary solvent mixtures containing NaClO₄ salt were investigated as electrolytes for sodium-ion batteries. The electrochemical performance of Na₄Fe₃(PO₄)₂(P₂O₇) cathodes was substantially improved when paired with an ethylene carbonate (EC)/propylene carbonate (PC)-based electrolyte. Our investigation revealed that EC/PC/1 M NaClO₄ exhibits superior oxidation durability at the cathode and is highly stable toward a Na-metal electrode.     

Identification of a new family of phosphate compounds,AIBII6(P2O7)2P3O10: structures of KMn6(P2O7)2P3O10 and AgMn6(P2O7)2P3O10

Two members of a new family of inorganic phosphates of general formula A^IB^II₆(P₂O₇)₂P₃O₁₀; KMn₆(P₂O₇)₂P₃O₁₀ (a=5.405(2), b=26.918(11), c=6.660(5), β=107.31(3)°, V=925.1(9) Å³, space group P2₁/m, Z=2, D_calc=3.481 Mg m⁻³, R=0.0377 for 2235 observed reflections) and AgMn₆(P₂O₇)₂P₃O₁₀ (a=5.424(7), b=26.97(4), c=6.627(9), β=106.81(7)°, V=928(2) Å³, space group P2₁/m, Z=2, D_calc=3.716 Mg m⁻³, R=0.0594 for 1577 observed reflections) have been synthesized and identified by single crystal X-ray diffraction. The isostructural complexes present an interesting comparison of silver and potassium bonding.     

Crystal structure and heat capacity of the mixed-valence trinuclear iron monoiodoacetate complex, [Fe(III)2Fe(II)O(O2CCH2I)6(H2O)3][Fe(III)3O(O2CCH2I)6(H2O)3]I

The crystal structure of a trinuclear iron monoiodoacetate complex was determined. Although it has been incorrectly characterized as [Fe₃O(O₂CCH₂I)₆(H₂O)₃], the correct chemical formula turned out to be [Fe(III)₂Fe(II)O(O₂CCH₂I)₆(H₂O)₃]-[Fe(III)₃O(O₂CCH₂I)₆(H₂O)₃]I (1). The two kinds of Fe₃O molecules (Fe(III)₂Fe(II)O and Fe(III)₃O) are crystallographically indistinguishable. All the Fe atoms are crystallographically equivalent because of a crystallographic threefold symmetry. Heat capacities of 1 seem to exhibit no thermal anomaly in the temperature range 5.5–309 K, although the valence detrapping phenomenon has been observed in this temperature range. This fact indicates that the valence-detrapping phenomenon in 1 occurs without any phase transition, leading 1 to a glassy state, probably because the crystal of 1 is just like a solid solution of distorted mixed-valence Fe(III)₂Fe(II)O molecules and permanently undistorted Fe(III)₃O molecules which may act as an inhibitor for a cooperative valence-trapping.     

Crystal structure and ionic conductivity of AgCr2(PO4)(P2O7)

Single crystals of a new phosphate AgCr₂(PO₄)(P₂O₇) have been prepared by the flux method and its structural and the infrared spectrum have been investigated. This compound crystallizes in the monoclinic system with the space group C2/c and the parameters are, a = 11.493 (3) Å, b = 8.486 (3) Å, c = 8.791 (2) Å, β = 114.56 (2)°, V = 779.8 (3) ųand Z = 4. Its structure consists of CrO₆ octahedra sharing corners with P₂O₇ units to form undulating chains extending infinitely along the [110] direction. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the Ag⁺ ions are located. The infrared spectrum of this compound was interpreted on the basis of P₂O₇^4? and PO₄^3? vibrations. The appearance of ν_sP–O–P in the spectrum suggests a bent P–O–P bridge for the P₂O₇^4? ions in the compound, which is in agreement with the X-ray data. The electrical measurements allow us to obtain the activation energy of (1.36 eV) and the conductivity measurements suggest that the charge carriers through the structure are the silver captions.     

A study on the thermal stability of uranyl phosphates (UO2)3(PO4)2, (UO2)2P2O7, and UO2(PO3)2 using a static non-isothermal method

A static, non iso-thermal method is used to investigate the stability of uranyl phosphates. The resulting oxygen partial pressures can be expressed as: (UO₂)₃(PO₄)₂, (1089–1280°K) log pO₂/atm = (−18480±400)/T+(13.11±0.33)(UO₂)₂P₂O₇, (979–1130°K) log pO₂/atm = (−27460±540)/T+(24.26±0.51)UO₂(PO₃)₂, (963–1118°K) log pO₂/atm = (−25320±680)/T+(22.58±0.66).Using these results, a part of the phase diagram UO_x (x = 2 to 3) − P₂O₅ is calculated.     

Low temperature heat capacity and magnetic properties of UF3

The low temperature heat capacity of UF(3) has been measured using an adiabatic low temperature calorimeter in the temperature range from 10 to 350 K. These data are complemented at the lowest temperature region with data obtained with a Quantum Design PPMS-14 device in the temperature range from 0.5 to 20 K. Good agreement between both techniques has been found, and from these experimental results the absolute entropy of UF(3) at 298.15 K has been determined as 126.8 ± 2.5 J K(-1) mol(-1). On the basis of the specific heat data and the magnetization measurements performed on a SQUID device, a transition at 1.59 K attributed to Curie temperature of a ferromagnetic transition has been found in this study. This observation makes UF(3) a unique compound with an unusually low ferromagnetic ordering temperature.     

Na7Y2(P2O7)2 (P3O10) – A New Layer and Tunnel Structure

A new layered phosphate, Na₇Y₂(P₂O₇) ₂(P₃O₁₀), containing both [P₂O₇]^4? and [P₃O₁₀]^5? groups, has been prepared. It crystallizes in the monoclinic space group P2/c with a = 16.205(4), b = 5.3746(9), c = 12.309(4) Å, β = 97.96(2)°, V = 1061.7(5) ų and Z = 2. The structure was solved and refined to R₁ = 0.0298 and wR₂ = 0.0698 for 1844 independent reflections with I > 2σ(I). It consists of layers of corner and edge-sharing YO₇ polyhedra, P₂O₇ and P₃O₁₀ groups. Each layer is built up from two parallel [YP₂O₇] slabs, held together by the P₃O₁₀ groups. This arrangement gives rise to intersecting tunnels within the layer. The Na⁺ cations are located in the tunnels and between the layers. Both P₂O₇ and P₃O₁₀ groups contain unshared oxygen atoms directed toward the interlayer space and toward the tunnels. The P₂O₇ groups show a staggered configuration. In addition to this original layered framework, the title compound provides the third example of a compound containing a mixed anion of [P₂O₇]^4? and [P₃O₁₀]^5?. The structure was compared with the two previously reported ones, containing such a mixed anion: NH₄Cd₆(P₂O₇) ₂(P₃O₁₀) [6] and Cs₂Mo₅O₂(P₂O₇)₃ · (P₃O₁₀) [7].