The compound Na2ZnV2O7 with an åkermanite-type structure has been synthesized. It has a tetragonal unit cell, a=8.2711(4), c=5.1132(2) Å, and crystallizes with P-421m symmetry, Z=2. Its crystal structure has been refined from a combination of X-ray and neutron powder diffraction data. The structure contains layers of corner-sharing VO4 and ZnO4 tetrahedra, the former in pairs forming pyrovanadate V2O7 units. The sodium atoms are positioned between the layers, with a distorted antiprismatic coordination of oxygen atoms.

New layered bismuth oxides Bi2(BiCaNa)m−1NbmO3m+3(m=2-4) with the Aurivillius type phase were successfully synthesized. The structures of the compounds have been studied by X-ray powder diffraction and refined by the Rietveld method. Bi2.25Ca0.5Na0.25Nb2O9(m=2) has an orthorhombic crystal structure with lattice constants a=5.4478(1) Å;b=5.4770(2) Å;c=24.883(8) Å, space group A21am (No. 36). Bi2CaNaNb3O12 and Bi2.25Ca0.5Na1.25Nb3O12(m=3) are orthorhombic with Fmmm(No. 69) space group and the unit-cell parameters a=5.4473(7) Å, b=5.4770(3) Å, c=32.722(6) Å and a=5.4574(7) Å, b=5.4884 (3) Å, c=32.711(6) Å, respectively. The structure of Bi2CaNa2Nb4O15(m=4) was found to be orthorhombic with parameters a=5.4584(8) Å, b=5.4833(3) Å, c=40.534(1) Å and was refined in the space group A21am (No. 36).

Recent developments at synchrotron X-ray beamlines now allow collection of data suitable for structure determination and Rietveld structure refinement at high pressures and temperatures on challenging materials. These include materials, such as dolomite(CaMg(CO3)2) that tends to calcine at high temperatures, and Fe-containing materials, such as the spinel MgFe2O4, which tend to undergo changes in oxidation state. Careful consideration of encapsulation along with the use of radial collimation produced powder diffraction patterns virtually free of parasitic scattering from the cell in the case of large volume high-pressure experiments. These features have been used to study a number of phase transitions, especially those where superior signal-to-noise discrimination is required to distinguish weak ordering reflections. The structures adopted by dolomite, and CaSO4, anhydrite, were determined from 298 to 1466 K at high pressures. Using laser-heated diamond-anvil cells to achieve simultaneous high pressure and temperature conditions, we have observed CaSO4 undergo phase transitions to the monazite type and at highest pressure and temperature to crystallize in the barite-type structure. On cooling, the barite structure distorts, from an orthorhombic to a monoclinic lattice, to produce the AgMnO4-type structure.

The X-ray Rietveld refinement technique was used to determine the structure and prepare X-ray powder reference patterns for the phases R2Cu9Ti12O36 (R=Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu). R2Cu9Ti12O36 belongs to the perovskite-related [AC3](B4)O12 family of structures, which are cubic with space group Im3. The lattice parameters of the R2Cu9Ti12O36 series range from a=7.377 57(2) Å, V=401.550(3) Å3 for R=Lu to a=7.399 87(3) Å, and V=405.202(4) Å3 for R=Nd. The trend of these lattice parameters parallels the “lanthanide contraction.” In the structure, R occupies the larger icosahedral A site of the ideal ABO3 perovskite structure, while Ti occupies the distorted octahedral B site. The Jahn-Teller cation Cu occupies the C site. The twelve oxygens surrounding Cu are arranged as three mutually perpendicular rectangles of different size. The smallest and largest rectangles are nearly squares. One-third of the R site is vacant, and the chemical formula can be written as [R2∕3X1∕3Cu3](Ti4)O12, where X=vacancy. The X-ray powder patterns of R2Cu2Ti12O36 have been submitted to ICDD for inclusion in the Powder Diffraction File (PDF).

The crystal structure of the perovskite phase KCaF3 has been redetermined at 4.2 and 300 K using powder neutron diffraction collected at the highest resolution. At both temperatures the phase was found to be orthorhombic in space group Pnma, with lattice parameters a=0.622 879(5) nm, b=0.870 031(7) nm, c=0.611 210(5) nm at 4.2 K, and a=0.621 488(6) nm, b=0.876 360(8) nm, c=0.616 481(6) nm at 300 K. The CaF6 octahedron is regular at both temperatures with octahedral rotations of 9.6° and 13.2° for the in-phase and anti-phase tilts, respectively, at 4.2 K. No evidence was found to support the recent revision of the space group from Pnma to the monoclinic space group B21∕m.

The measurement of lattice parameters using the Le Bail method was shown to be inappropriate for a complex, low symmetry, structure, even with high resolution synchrotron diffraction data. The method failed as a result of ambiguous indexing in the absence of constraints on diffraction intensities, that arise when a structural model is used, combined with the large number of reflections. A caution for the use of the Le Bail and other whole-powder pattern decomposition methods is presented, particularly for high reflection density data.

The recent advances in levitation methods for materials processing now enable structural, thermo-physical property, and phase transition studies to be made on high temperature solids and liquids without container contamination. These studies have led to new insights into the liquid state and have revealed how local order in the liquid can dictate phase formation. In this article, levitation techniques are briefly discussed, focusing most on electrostatic levitation. Recent synchrotron studies of electrostatically levitated undercooled Ti–Zr–Ni liquids are presented, which demonstrate that developing icosahedral short-range order in the liquid causes the nucleation of a metastable icosahedral quasicrystal instead of the stable tetrahedral Laves phase. In addition to providing the first experimental proof of a half-century-old hypothesis linking the order of the liquid with the nucleation barrier, these data raise new questions about the general applicability of the thermodynamic model assumed in the classical theory of nucleation. The combination of electrostatic levitation and synchrotron high-energy x-ray diffraction also allows rapid and accurate determinations of phase diagrams for high temperature materials. This is demonstrated usingTi–Fe–Si–O as a case study. This new technique, then, is of practical as well as basic importance.

The Nowotny chimney–ladder compound VGe1.82 was redetermined from powder diffraction data and modelled with the incommensurately modulated composite approach. The dimensions of the tetragonal unit subcells are a=5.9015(3) Å, cGe=2.6916(2)Å, and cV=4.9080(2)Å and the one-dimensional modulation vectors are qGe=0.45159(1)[001]* and qV=0.17656(1)[001]*. Comparison is made with a previous reported commensurate approximation of the structure with a 31-fold cGe axis.

From 1967 to 2000 Daniel Louër of the Department of Crystal Chemistry, University of Rennes, and J. Ian Langford of the Department of Physics, University of Birmingham, collaborated in studying structural imperfections by means of high-resolution X-ray powder diffractometry. They contributed to the theory and practice of line profile analysis and investigated the microstructure of a variety of nanocrystalline materials. Although many of the projects undertaken were part of the research programme at Rennes to investigate the mechanisms of solid-state reactions, the work is relevant in other fields of materials science.

Potassium tetraperoxomolybdate (VI) K2[Mo(O2)4] was prepared, and its X-ray powder diffraction pattern was recorded at low temperature (258 K). The unit cell parameters were refined to a=10.7891(2) Å, α=64.925(3)°, space group R−3c (167), Z=6. The compound is isostructural with potassium tetraperoxotungstate (VI) K2[W(O2)4] (Stomberg, 1988). The sample of K2[Mo(O2)4] was characterized by analytical investigations, and the results of crystal structure refinement by Rietveld method are presented; final RP and RWP are 9.79% and 12.37%, respectively.

In situ high-temperature X-ray diffraction (XRD) data have been collected for silver behenate, CH3(CH2)20COOAg. In the absence of development chemistry silver behenate exhibits four phase transformations when heated from room temperature to 200 °C. Combining XRD and differential scanning calorimetry (DSC) results, the phase transformation temperatures and phase types have been determined. Types I, II, and III forms of silver behenate are found to be crystalline phases, whereas Types IV and V forms are liquid crystal phases.

A short history of the developments of the successive dichotomy method for powder pattern indexing is presented. In the first computer powder indexing programs (P1 and P2), only high lattice symmetries, down to orthorhombic, were considered [Louër and Louër, J. Appl. Crystallogr. 5, 271–275 (1972)]. Later on, an extension to the monoclinic symmetry was reported in DICVOL, including a partition of the volume space to first search solutions with smaller unit cell volumes [Louër and Vargas, J. Appl. Crystallogr. 15, 542–545 (1982)]. However, CPU times were slow in some monoclinic examples. A thorough mathematical analysis resulted in a significant optimization of the CPU times [Boultif and Louër, J. Appl. Crystallogr. 24, 987–993 (1991)]. Simultaneously, the method is extended to triclinic lattices. The stages of development of the various versions of the DICVOL program are described, with a particular emphasis on DICVOL91 (Boultif and Louër, 1991) and DICVOL04 [Boultif and Louër, J. Appl. Crystallogr. 37, 724–731 (2004)]. This article is written to testify to and emphasize the major role played by Daniel Louër, who introduced the successive dichotomy method and continued to its evolution and optimization over almost 40 years.

The ternary nitridotungstate Li6WN4 has been synthesized via the solid state reaction of lithium subnitride, Li3N, with W under nitrogen. High quality X-ray powder diffraction data were collected for the crystal-structure determination. Li6WN4 crystallizes in the tetragonal system, space group P42∕nmc, with cell parameters a=6.6759(3) Å and c=4.9280(3) Å, Z=2. Preliminary thermal stability measurements of Li6WN4 show that it is sensitive to moisture, even at room temperature, and decomposes at high temperatures below 1000 °C under flowing nitrogen.

Single-phase (Ho0.50Ca0.50)MnO3 has been successfully prepared by means of solid state reaction at high temperature. Its crystal structure, as well as those of Cr-doped samples(Ho1−xCax)(Mn1−yCry)O3, has been refined by the Rietveld method, using X-ray powder diffraction data. All the examined compounds crystallize in the Pnma space group with a distorted perovskite-type structure. The distortion of the BO6 octahedra, due to the Jahn–Teller Mn3+ ionic species, decreases with the Cr content. Bond valence sum calculations were carried out using the refined results.

Phase composition estimates by X-ray powder diffraction and Rietveld analysis are becoming more widely used in the cement industry. The ASTM C01.23 Compositional Analysis subcommittee developed test method C 1365, “Standard Test Method for Determination of the Proportion of Phases in Portland Cement and Portland-Cement Clinker Using X-Ray Powder Diffraction Analysis.” A round-robin analysis involving 11 laboratories was initiated to assess the precision and bias of this approach and to develop guidelines for Rietveld analysis of hydraulic cements. Four cements were prepared using NIST SRM clinkers spiked with known amounts of one or more of the following minerals: gypsum, bassanite, anhydrite, and calcite. Specimens were provided with instructions that laboratories analyze the whole cement, collect data in triplicate, and repack the specimen for each run. The results of the round robin were used to estimate interlaboratory and intralaboratory precision and bias of phase abundance determinations. The results show an improvement over previous cement round-robin studies utilizing traditional internal-standard-based, peak-area-measurement methods.

The low-cristobalite-type modification of Al0.5Ga0.5PO4 is prepared by annealing the amorphous precipitate of stoichiometric phosphate at 1300 °C. The phase purity of the sample is ascertained by powder X-ray diffraction. The crystal structure is refined by Rietveld refinements of the neutron and X-ray diffraction data of the polycrystalline powder. This compound crystallizes in an orthorhombic lattice with unit cell parameters, a=7.0295(8), b=7.0132(8), and c=6.9187(4) Å, V=341.08(6) Å3, Z=4 (Space group C 2221, No. 20). The crystal structure analysis reveals the random distribution of the Al3+ and Ga3+ having tetrahedral coordination with typical M–O (M=Al3+:Ga3+) bond lengths as 1.74 Å. Similarly, the P5+ have tetrahedral coordination with typical P–O bond lengths 1.52–1.54 Å. The Mo4 and PO4 tetraheda are linked by common corners forming a three-dimensional framework lattice. The details of the crystal structure are presented in this paper.

Ni20[(C6H8O4)20(H2O)8]∙33H2O, a new nickel(II) 3-methylglutarate, was prepared hydrothermally (180 °C, 48 h, autogenous pressure) from a 1:1.5:2:180 mixture of nickel (II) sulphate hexahydrate, 3-methylglutaric acid, sodium hydroxide, and water. It crystallizes in the cubic system (space group P4332, Z=1) with a=16.8488(5) Å and V=4783.1(4) Å3. Its structure was solved from conventional X-ray powder diffraction data. It presents a three-dimensional network of edge-sharing nickel octahedra, lined by deprotonated organic anions. This remarkable oxide network with corrugated 20-membered rings is constructed from homochiral helices. The rings intersect each other to generate large crossing channels full of water along [111].