The incommensurately modulated structure of Bi2Sr2Eu1.3Ce0.7Cu2O10.17, with a = 5.4752(4) Å, b = 5.4522(3) Å, c = 17.860(1) Å, Z = 2, was refined by the GJANA program [Gao et al., Acta Cryst. A 49, 141 (1993)] from X-ray powder data in C:C2mb: 111 four-dimensional space group (Rov = 0.064, Rm = 0.041, Rsat = 0.202, Rp = 0.049, Rwp = 0.065). Displacive modulation parameters of all cations and oxygen atoms in the Bi-layer were involved in the refinement. Obtained results including the modulation parameters are in agreement with those found for the similar phase Bi2Sr1.7Nd1.8Ce0.5Cu2O10+δ from single-crystal data [Mironov et al., J. Solid State Chem. 109, 74 (1994)].

A resident powder diffractometer control program is described, which allows independent use of the PC for other programs during data collection. The control program and a simple interface card were developed for the case when a PC is used to automate the DRON type diffractometers.

Reaction of tungsten (W) with SF6 has been studied using two types of samples. The first type (type I) consisted of rods fabricated by a drawing process and the second type (type II) consisted of square plates cut from a hot pressed billet. After the corrosion experiments, scanning electron microscopy (SEM) examination of the type I sample indicated the presence of deep pits parallel to the rod axis. X-ray analysis of these rods showed preferred orientation. Pole figure measurement was subsequently conducted to quantify the preferred orientation by using neutron diffraction. A significant orientation effect on the corrosion process was found, possibly originating from the considerable granular elongation parallel with the rod axis produced during the fabrication process. In contrast, the type II sample showed no directional corrosion and insignificant preferred orientation.

Improved powder X-ray diffraction (XRD) data for liottite and sacrofanite, two members of the cancrinite group of minerals, were obtained using a rotating anode diffractometer. The cell parameters of liottite are a = 12.8575(3), c = 16.0905(6) Å, and the space group is ; the strongest reflections are at 4.834(38), 3.783(12), 3.714(100), 3.312(91), 2.784(13), 2.682(26), 2.470(17), and 2.143(27) Å. The cell parameters of sacrofanite are a = 12.8945(4) and c =74.2128(37) Å, and the possible space groups are P63/mmc, P63mc, and ; the strongest reflections are at 11.18(23), 3.757(25), 3.723(100), 3.488(27), 3.302(62), 2.651(31), 2.645(30), and 2.149(18) Å. The new data include an increased number of indexed peaks and empirical formulae that differ from the reference data (PDF 29-1187 and PDF 35-653, respectively).

A new amine zinc hydroxide nitrate has been synthesized and investigated by means of X-ray powder diffraction. The monoclinic unit cell dimensions are a = 20.781(3) Å, b = 6.2151(9) Å, c = 5.4952(6) Å, β = 92.24(1)° (space group C2/m with Z = 2). The crystal structure has been refined by the Rietveld method using the structure of the related dihydrated phase as a starting model (Rp = 0.092 and RF = 0.068 for 372 reflections). The structure is characterized by octahedra [Zn(OH)6] describing a brucite-type layer, with one-quarter of the metal atoms missing, and by tetrahedra [Zn(OH)3(NH3)] located above and below the empty octahedra. The complex positive sheet has the formula [Zn3octa(OH)8Zn2tetra(NH3)2]2+ and the cohesion of the structure is realized through hydrogen bonding.

The measurement of x-ray diffraction line intensities is the basis for quantitative phase analysis (see for example, Chung (1974), Davis (1986), and Hubbard and Snyder (1988)). While there are many sources of error in such measurements, in recent years computer automation of powder diffractometers and associated analytical software has made such measurements more practical and accurate. For example, profile fitting software has made it possible to determine integrated peak areas and to deconvolute overlapping lines. Another problem which affects quantitative analysis is the systematic error in instrument sensitivity as a function of 20 diffraction angle. This effect has been partially responsible for poor reproducibility of relative intensities between laboratories (Schreiner and Kimmel (1987), and Jenkins and Schreiner (1989)). But, because the error is systematic, corrections may be made by using a standard such as the National Institute of Standards and Technology SRM 1976 alumina plate (NIST 1991). These and other advances have led to a renewed interest in the determination of I/Ic (also called RIR - Reference Intensity Ratio) values for crystalline substances (e.g., Snyder (1992)). I/Ic is defined as the ratio of the intensity of the strongest line of an analyte to the corundum (113) line when the analyte is mixed 50:50 by weight with corundum. We present here a standard procedure used in our laboratory to experimentally measure I/Ic values, and which explicitly incorporates profile fitting and instrument sensitivity corrections. The procedure is written in the format of an ASTM (American Society for Testing and Materials) standard test method, however, inter-laboratory round robin tests have not been carried out to determine precision and bias associated with the method. While the method calls for corundum as the internal standard, another standard material, s, may be used, in which case the procedure will result in a ratio I/Is. Hubbard and Snyder (1988) have shown how to convert between I/Is and I/Ic. This method is based on the procedure routinely published in NBS Monograph 25 until 1986. It is augmented with corrections for the angularly dependent instrument sensitivity and with calculations of I/Ic for both variable and fixed divergence slit configurations. A Quattro Pro spreadsheet is used in our laboratory to do the calculations. An example of the spreadsheet is given in the appendix for one of two I/Ic runs of MgCO3. We also utilize the corundum in the I/Ic runs as an internal standard to determine displacement error corrections for preparation of digitized patterns of pure analyte phases. These patterns are submitted to the International Centre for Diffraction Data for inclusion in a whole pattern data file planned for some time in the future. The notation used here is the standard notation developed for the RIR method by Hubbard and Snyder (1988) and systematically extended by Snyder (1992). A table of the notation is given in the Terminology section below.

Detailed procedures for solving small crystal structures ab initio with the maximum-entropy (ME) methods using X-ray powder diffraction data are described by determining the structure of the low-pressure phase of magnesium boron nitride, Mg3BN3(L), which was previously solved by one of the authors and co-workers using the Patterson method and the direct methods. The simple ME method devised by Gull, Livesey, and Sivia failed to correctly phase the structure-factor data, leading to noninterpretable electron-density maps. This method, maximizing the entropy under the constraints of the observed structure factors with subsequent incorporation of strong extrapolates in the basis set, trapped the solution in a local entropy maximum, from which there is no way to move. The multisolution method of phase determination by entropy maximization and likelihood evaluation, developed by Bricogne and Gilmore, successfully located all the Mg, B, and N atoms in one cycle of phase extension. The correct solution had a highest log-likelihood gain, but a minimum entropy, among the multisolutions generated by phase permutation.

New solid solution phases in the (Y,Ca)(Cr,Co)O3 system have been synthesized and characterized by powder X-ray diffraction. The selected compositions in this system were prepared by the modified Pechini method. Powder-diffraction patterns were prepared.

The crystal structure of the tysonite-type superstructure of β-PrF3 has been studied by X-ray powder diffraction and high-energy electron diffraction from single crystals. The crystal data are: a = 7.0795(1) Å, c = 7.2380(2) Å, Z = 6, hexagonal system, space group (No. 165), ρcalc = 6.28 g cm−3. Atomic parameters and interatomic distances are presented from the final refinement with Rconv = 1.72%.

Quantitative determination of phase abundances using X-ray powder diffraction is a technique in wide use today. Of the various methods employed, the Chung, or RIR method, is one of the most common because it can provide reliable results for all sample types. However, improvements can be made to the Chung method of analysis for phases which exhibit large chemical or preferred orientation effects. These effects can often be accommodated by using intensity regions that encompass several reflections, by averaging intensities from nonparallel reflections, or by using RIR values that are allowed to vary based on a predetermined functional relationship. To accommodate the effects of preferred orientation and variable composition in feldspars, RIR values versus the intensity ratio between two peaks of feldspar standards mixed with corundum have been determined. Curves of RIR have been formulated for: (1) feldspar RIR13.0−14.0° versus the intensity ratio (13.0–14.0° 2θ intensity region/27.0–28.75° 2θ intensity region); (2) feldspar RIR23.6° peak versus the intensity ratio (23.6° 2θ peak/27.0–28.75° 2θ intensity region); and (3) clinoptilolite RIR020 versus (020 reflection/22.1–23.0° 2θ intensity region). For example, RIR values for the highly variable 13.0–14.0° 2θ region for feldspar can be improved such that the quantitative results produced has a standard deviation of only 15% instead of 53% using a fixed-average value. From these curves, improved RIR values can be obtained for the quantitative analysis of unknowns. Additionally, intensity ratios can be determined between two peaks of a phase so that given the intensity of one peak, the intensity of the other peak can be readily calculated. This allows for subtraction of the intensity of a peak from one phase overlapping a peak from a second phase which is to be used for quantitative analysis but which cannot be decomposed by profile fitting.

A comprehensive review of phases found in the Sr–Nd–Cu–O system which contains the high Tc superconductor phase Sr1−xNdxCuO2 has been prepared. This paper summarizes the crystal structures reported in the literature and the X-ray powder diffraction patterns reported in the ICDD Powder Diffraction File (PDF). In order to supplement the PDF with new patterns, calculated X-ray powder diffraction patterns generated from reported structures are provided for five ternary oxides: Sr0.86Nd0.14CuO2, SrNdCuO3.5, Sr6Nd3Cu6O17, Sr2NdCu2O5.66, and Sr1.2Nd1.8Cu2O6.