Modern powder diffraction employing computer-controlled diffractometers now allows quantitative analytical methods to use the whole diffraction trace rather than only individual peaks. Two such methods are in common use: the Rietveld method, which refines the crystal structures of the component phases as part of the matching calculation, and the pattern-fitting method, which uses reference patterns from a database. Potential accuracies of these methods seems to be around 1% absolute. The most severe limitation on the potential accuracy of these methods is particle statistics, which has been reviewed in considerable detail.

X-ray powder diffraction is one of the two principal methods used for the routine analysis of free SiO2 for monitoring silica in the industrial workplace. During late 1996 and early 1997, a questionnaire was prepared and distributed to all the analytical laboratories on the American Industrial Hygiene Association (AIHA) list of accredited facilities that indicated they did analyses for silica. This report is based on the responses to that questionnaire with comments from the author on the responses and recommendations that suggest themselves from the responses.

Retained austenite is an important characteristic of properly heat-treated steel components, particularly gears and shafts, that will be subjected to long-term use and wear. Normally, either X-ray diffraction or optical microscopy techniques are used to determine the volume percent of retained austenite present in steel components subjected to specific heat-treatment regimes. As described in the literature, a number of phenomenological, experimental, and calculation factors can influence the volume fraction of retained austenite determined from X-ray diffraction measurements. However, recent disagreement between metallurgical properties, microscopy, and service laboratory values for retained austenite led to a re-evaluation of possible reasons for the apparent discrepancies. Broad, distorted X-ray peaks from un-tempered martensite were found to yield unreliable integrated intensities whereas diffraction peaks from tempered samples were more amenable to profile fitting with standard shape functions, yielding reliable integrated intensities. Retained austenite values calculated from reliable integrated intensities were found to be consistent with values obtained by Rietveld refinement of the diffraction patterns. The experimental conditions used by service laboratories combined with a poor choice of diffraction peaks were found to be sources of retained austenite values containing significant bias.

X-ray powder diffraction investigation of the new high temperature polymorphs beta- and gamma-CaTeO3 and gamma- and delta-CaTe2O5 and picnometric measurements of the room temperature phases of the two compounds have been carried out. The study led to the elucidation of their unit cell structures and assignment of entirely new lattice types and parameters to the room temperature phases of CaTeO3 and CaTe2O5 in contrast and supersession to the existing structural information. The results are as follows: CaTeO3 has only one stable phase at room temperature and temperatures up to 882 °C, i.e., α- and has a triclinic unit cell with a=4.132±0.003 Å, b=6.120±0.006 Å, c=12.836±0.013 Å, α=121.80°, β=99.72°, γ=97.26°. The first high temperature phase stable between 882 and 894 °C, i.e., β-CaTeO3, has a monoclinic lattice: a=20.577±0.007 Å, b=21.857±0.009 Å, c=4.111±0.002 Å, β=96.15°, while the next phase stable above 894 °C, i.e., γ-CaTeO3, has a hexagonal unit cell with parameters: a=14.015±0.0001 Å, c=9.783±0.001 Å, c/a=0.698. CaTe2O5 has one stable phase at temperatures up to 802 °C, i.e., α-CaTe2O5 with a monoclinic lattice and parameters: a=9.069±0.002 Å, b=25.175±0.007 Å, c=3.366±0.001 Å, β=98.29 °. The first high temperature phase stable in the range 802–845°, i.e., β-CaTe2O5, is monoclinic with unit cell parameters: a=4.146±0.001 Å, b=5.334±0.002 Å, c=6.105±0.002 Å, β=98.362 °; the next higher temperature phase stable over 845–857 °C, i.e., γ-CaTe2O5, has an orthorhombic unit cell with: a=8.638±0.001 Å, b=9.291±0.001 Å, c=7.862±0.001 Å and the highest temperature solid phase stable above 857 °C, i.e., δ-CaTe2O5 has a tetragonal unit cell with a=5.764±0.000 Å, c=32.074±0.020 Å, c/a=5.5637.

The structure of the new Y0.8Ca0.2Ba1.8La0.2Cu3Oy (YBLCO) compound was obtained at 298 K from X-ray powder diffraction data and refined by the Rietveld technique. YBLCO has a structure isotypical with YBa2Cu3Oy (YBCO) at room temperature. The crystal data are: Y0.81Ca0.19Ba1.8La0.2Cu3O7.08, Mw=657.69, orthorhombic system, space group Pmmm, a=3.8731(1) Å, b=3.8249(1) Å, c=11.6602(3) Å, V=172.740(13) Å3, Z=1, dx=6.325 g/cm3; the structure was refined with 37 parameters to Rwp=7.66%, Rp=5.86%, and Rexp=5.11% for 2001 data points. Moreover, the proportions of Ca and La were refined to be 0.19 and 0.2, in agreement with the stoichiometric proportion of 0.2.

Improved powder X-ray diffraction (XRD) data for franzinite, the ten-layer member of the cancrinite group of minerals, were obtained using an automated parallel-beam powder diffractometer with a capillary mount. The cell parameters of franzinite were found to be a=12.8976(3) Å, c=26.5040(8) Å, V=3818.2(2) Å3 in space group P321, while the strongest reflections were at 3.725(100), 3.809(65), 3.562(56), 3.586(55), 2.662(42), 2.150(31) and 3.302(30) Å. The new results include an increased number of indexed peaks, improved figures-of-merit with respect to PDF 30-1170 and intensities validated by Rietveld refinement.

Powder X-ray diffraction data are reported for RE6UO12 (RE=Eu, Gd, and Dy). The powders were prepared by a solution combustion method using urea as fuel. All compositions exhibit a rhombohedral structure with hexagonal unit cell parameters of a=1.012 67 (9) nm, c=0.9601 (1) nm for Eu6UO12; a=1.008 78 (6) nm, c=0.954 24 (7) nm for Gd6UO12; and a=0.998 06 (7) nm, c=0.944 03 (8) nm for Dy6UO12. The diffraction patterns of all the compounds are indexed on the R3¯ space group with Z=3. The a and c values decrease with increasing atomic number of the rare earth ion.

The anhydrous acid strontium oxalate Sr(HC2O4)⋅½(C2O4) was obtained by thermal decomposition of the hydrated acid strontium oxalate Sr(HC2O4)⋅½(C2O4)⋅H2O. This non-hygroscopic compound crystallizes in the space group P 21/c (No. 14) with unit cell parameters: a=0.796 61(7) nm, b=0.9205(1) nm, c=0.731 98(8) nm, and β=102.104(8)°. Final refinement of the X-ray powder data yielded RB=3.2% and Rwp=11.1% (background-corrected data). In this structure, Sr is eight-fold coordinated by O. These polyhedra are connected together by edge-sharing to form two-dimensional (2D) layers along the bc-plane, which means that there is an increased dimensionality from 1D to 2D with decreasing water content of the acid oxalates.

A detailed neutron powder diffraction study of the atomic structure of α-Bi2O3 at high temperatures using the Rietveld method was performed to clarify the nature of the unusual magnetic behavior and the origin of the high temperature dielectric anomalies of α-Bi2O3 in the temperature interval 300–700 K. Analysis of obtained experimental data shows that there are no evidence of a structural phase transition in α-Bi2O3 between 295 and 660 K. The observed high temperature dielectric anomalies in α-Bi2O3 are evidently governed by changes in the electron subsystem of the bismuth oxide.

X-ray powder diffraction data are reported for a series of multipyrazole compounds in this paper. This work shows that the unit cell dimensions determined by single crystal agree well with those of powder diffraction analysis.