Low-temperature structural phase transition in synthetic libethenite Cu2PO4OH

Low-temperature structural properties of the synthetic mineral libethenite Cu₂PO₄OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry (a=8.0553(8) Å, b=8.3750(9) Å, c=5.8818(6) Å at 180 K) to the P2₁/n symmetry (a=8.0545(8) Å, b=8.3622(9) Å, c=5.8755(6) Å, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P2₁/n–to–Pnnm transition may be a general feature of the adamite-type compounds, M₂XO₄OH.     

Stereoselective Ring Opening of Electronically Excited Cyclohexa-2, 4-dienones: Cause and effect

The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction).     

Crystal structure of double vanadates Ca9 R(VO4)7. II. R = Tb, Dy, Ho, and Y

Crystal structures of the compounds Ca₉ R(VO₄)₇ (R = Tb (I), Dy (II), Ho (III), and Y (IV) have been studied by the method of the full-profile analysis. All the compounds are crystallized in the trigonal system (sp. gr. R 3 c, Z = 6) with the unit-cell parameters (I) a = 10.8592(1), c = 38.035(1), V = 3884.2(2) ų; (II) a = 10.8564(1), c = 38.009(1) Å, V = 3879.6(2) ų, (III) a = 10.8565(1) and c = 37.995(1) Å, V = 3878.3(2) ų, and (IV) a = 10.8588(1), c = 37.995(1) Å, V = 3879.9(2) ų. In structures I–IV, rare earth and calcium cations occupy three positions—M(1), M(2), and M(5). Rare earth cations occupy the R ³⁺ positions almost in the same way: 2.7–2.6(2) cations in the M(1) position; 2.7–2.3(2) cations in the M(2) position, and 0.6–1.0(1) cation in the M(5) position. At the same time, the occupancy of the M(5) position regularly increases with a decrease of the R ³⁺ radius.     

New type of borophosphate anionic radical in the crystal structure of CsAl<Subscript>2</Subscript>BP<Subscript>6</Subscript>O<Subscript>20</Subscript>

The crystal structure of a new borophosphate CsAl₂BP₆O₂₀ obtained by spontaneous crystallization in a multicomponent Cs–Cu–B–P–O system is determined by X-ray diffraction (a = 11.815(2), b = 10.042(2), and c = 26.630(4) Å; space group Pbca, Z = 8, V = 3159.5(10) ų; R₁ = 0.043). A new type of borophosphate anionic 2D radical characterized by the lowest B: P = 1: 6 ratio and containing P₃O₁₀ phosphate groups is found in the compound. A mixed-type anionic framework consisting of vertex-sharing BO₄ and PO₄ tetrahedra and AlO₆ octahedra is distinguished in the structure. Large cesium atoms are located in the channels of the framework. Topological relationships are revealed between the structures of the CsAl₃(P₃O₁₀)₂ and CsAl₂BP₆O₂₀ phases having different cationic compositions. These compounds can be considered quasi-polytypic phases.     

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

The Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method using KOs₂O₆ as a host. The composition was identified as Na_1.4Os₂O₆·H₂O by electron probe micro-analysis, thermogravimetric analysis, and structural analysis using synchrotron X-ray diffraction. Na_1.4Os₂O₆·H₂O crystallizes in a regular pyrochlore structure with some defects (space group: Fd-3m, a=10.16851(1) Å). Electrical resistivity, heat capacity, and magnetization measurements clearly showed absence of superconductivity down to 2 K, being in large contrast to what was found for the β-type pyrochlore superconductor AOs₂O₆ (A=Cs, Rb, and K). The Sommerfeld coefficient is 22 mJ K⁻² mol⁻¹, being the smallest among AOs₂O₆. A magnetic anomaly at ∼57 K and associated magneto-resistance (+3.7% at 2 K in 70 kOe) were found.     

BiScO3: centrosymmetric BiMnO3-type oxide

With neutron powder diffraction, electron diffraction, and second-harmonic generation, we have shown that BiScO3 has a structure closely related to that of multiferroic BiMnO3, but BiScO3 crystallizes in the centrosymmetric space group of C2/c. These results bring up a question about the origin of ferroelectricity in BiMnO3. BiScO3 may serve as a model system to understand the role of Mn3+ ions in the ferroelectricity of BiMnO3.     

Comment on “Impedance spectroscopy study and ground state electronic properties of In(Mg1/2Ti1/2)O3 (Physica B 406 (2011) 1081–1087)” and related works

In this comment, we demonstrated that some reports about synthesis and properties of double In-based perovskites, In(Mg_1/2Ti_1/2)O₃, In(Ni_1/2Zr_1/2)O₃, and In(Co_1/2Ti_1/2)O₃, are incorrect. Mixtures of different known oxides were investigated instead of the claimed new compounds. We also tried to prepare In(Ni_1/2Zr_1/2)O₃, In(Ni_1/2Ti_1/2)O₃, and In(Zn_1/2Mn_1/2)O₃ using a high-pressure method (at 6 GPa and 1580 K) and found that these compounds are not formed. Only in the In₂O₃–NiO–MnO₂ system, a new perovskite phase is formed using the high-pressure preparation method.