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We have studied the effects of the isoelectronic substitution of Ru for Fe in polycrystalline samples of the spin density wave (SDW) material PrFeAsO. Crystal structures from powder X-ray diffraction at room temperature and transport properties from 2 to 300 K are reported. The SDW is completely suppressed upon Ru substitution. The distortion of the tetrahedral coordination environment of the transition metal site increases as the Ru concentration increases, which may be related to the absence of superconductivity above 2 K. Band structure calculations show that the larger size of Ru 4 d orbitals is primarily responsible for the suppression of magnetism as Ru is substituted into the Fe layer. The experimental results indicate that long-ranged magnetic order of Pr moments is suppressed at Ru concentrations as low as 10%.

To elucidate the phase transition at 115 K in the fresnoite-type compound K 2 V 3 O 8 , we undertook temperature-dependent neutron powder diffraction and single-crystal X-ray diffraction (XRD). For structure refinements in the nominal space group P 4 bm , the most dramatic change is evidenced by the a cell edge, which initially expands on cooling, then abruptly begins to contract at 115 K. The c cell edge contracts monotonically. The atomic displacement parameters (ADPs) also deviate from their expected temperature dependence at 115 K, where the oxygen atoms in the vanadium oxide plane exhibit an increase in apparent positional disorder. Similar changes in lattice parameters and ADPs are observed from the single-crystal XRD refinements. Below 115 K, weak superlattice reflections are clearly evident in XRD patterns recorded by a CCD detector, and these extra reflections can be indexed with the wave vector ±1/3〈110〉*+1/2 c *. Possible space groups for the modulated structure are P 4 2 bc and P 4 nc .

High-purity Rb2V3O8 has been grown and temperature-dependent electron and single-crystal X-ray diffraction used to carefully investigate its fresnoite-type reciprocal lattice. In contrast to other recently investigated representatives of the fresnoite family of compounds, Rb2V3O8 is not incommensurately modulated with an incommensurate basal plane primary modulation wave vector given by q∼0.3 〈110〉*. A careful low-temperature electron diffraction study has, however, revealed the existence of weak incommensurate satellite reflections characterized by the primitive primary modulation wave vector q1∼0.16c*. The reciprocal space positioning of these incommensurate satellite reflections, the overall (3+1)-d superspace group symmetry, as well as the shapes of the refined displacement ellipsoids determined from single-crystal XRD refinement, are all consistent with their arising from a distinct type of condensed rigid unit modes (RUMs) of distortion of the Rb2V3O8 parent structure.

A new structure-property relationship links atomic displacement parameters (ADP) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-like compounds, in which one of the atom types is weakly bound and rattles within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the rattler, and the temperature dependence of the heat capacity. X-ray crystallography data, reported in the literature, are used to apply this analysis to several promising classes of thermoelectric materials.

Polycrystalline vanadium oxynitrides have been prepared by heat-treating V 2 O 5 at high temperature in a flowing ammonia atmosphere. Single-phase cubic samples, with the rock salt structure, were produced by nitridation at 600–700°C. Powder diffraction data from neutrons at two wavelengths and Cu K α X-rays of these oxynitrides were analyzed using the Rietveld method, but strong correlation among the atomic displacement parameters, site occupancies, and the N/O ratio did not allow a refinement of unique compositions. Measured densities and cell volumes were used to limit the possible compositional space for each sample, and these were further limited by the charge neutrality requirement. The electrical resistivity of the single-phase sample is about 2 × 10 −3 Ω·cm and is weakly temperature dependent below room temperature. Magnetic susceptibility measurements show no evidence of magnetic ordering and yield a magnetic moment of 0.25 μ B per V atom. Electrochemical lithium intercalation measurements indicate that only a small concentration of lithium ions were inserted into the cathode due to the close-packed NaCl structure of cubic vanadium oxynitride.

A crystalline form of lithium phosphorus oxynitride, Li 2.88 PO 3.73 N 0.14 , has been prepared by solid state reaction between Li 3 N and LiPO 3 under a flowing N 2 atmosphere. The structure of the oxynitride was refined by Rietveld analysis of neutron powder diffraction data using the orthorhombic unit cell of γ-Li 3 PO 4 with space group Pmnb . High-performance liquid chromatography measurement indicates that most nitrogen substitutes for oxygen to form PO 3 N structural units with small concentrations of P-N[]P due to some Li ↔ P disorder in the structure. The ionic conductivity of Li 2.88 PO 3.73 N 0.14 (σ25°C ∼ 10 -13 S · cm-1) is several orders of magnitude higher than that of γ-Li 3 PO 4 (σ 25°C ∼ 10 -18 S · cm -1 ).

High-performance liquid chromatography (HPLC) measurements on crystalline and glassy Na[sub 4]NbP[sub 3]O[sub z] prove that the crystalline phase is a pyrophosphate and that the glassy material contains a distribution of phosphate anions with anions up to five PO[sub 4] tetrahedra in length. Powder X-ray diffraction data for a new trimetaphosphate crystalline phase with the composition Na[sub 3]NbP[sub 3]O[sub x] are also reported.

Lead pyrophosphate, Pb2P2O7, crystallizes in the triclinic space group P 1 (Z = 4) with a = 6.914(2), b = 6.966(2), c = 12.751(4) A; α = 96.82(3), β = 91.14(3), γ = 89.64(3)°; and V = 612.0(6) A3. Structural refinement data were collected using an automated diffractometer with MoKα radiation. The lead pyrophosphate structure was refined by a full matrix to an R of 0.069 (Rw = 0.067) using 2637 unique reflections. The structure has two unique diphosphate groups that are repeated by lattice translations to form sheets of diphosphate groups. The P2O7 groups, dichromate type, are eclipsed to within 9.4 and 13.5°. The Pb2+ ions are eight- and nine-coordinated to oxygen atoms with average experimental interatomic distances of 2.695 and 2.767 A, respectively.