This note discusses the use of the powder-diffractometer intensity-response function reference standard to be released shortly by the National Institute of Standards and Technology (NIST) as a Standard Reference Material (SRM). Its purpose is to encourage use of the standard and to stimulate discussion and comments from readers with regard to the procedure for its use. Comments may be addressed to either of the authors.

Pearson VII functions, some of the most useful descriptions of the intensity distribution within the X-ray powder reflection, have been used to study distortion in the perovskite-type structure of KMnF3. Separate full-widths, Δ, at half-maximum intensity, and Pearson exponents, m, were taken for the low- and high-angle sides of the profiles. The background was assumed to be linear. For the distorted structure, summation was made over all overlapping lines that might possibly contribute to the observed profile. Measurements were performed using a powder diffractometer with a specially adapted electronic system consisting of an automatic data recorder and a method, developed at this laboratory, for transferring data to an IBM PC/AT computer. By these means it could be shown that at 10° K the crystal structure of KMnF3distorts from cubic to monoclinic.

With the Powder Diffraction File (1988), twelve different numerical search manuals with the number of entries per phase from one to four were used to identify the 237 experimental X-ray powder diffraction data sets collected from visually measured 57.3 mm diameter Debye-Scherrer films. Eighty-four percent of the experimental X-ray powder diffraction data have the same strongest reflection as the data in the Powder Diffraction File. For a single-phase unknown the most efficient numerical search manual type is a single entry per phase if used correctly and systematically; however, multiple entries do help in some instances. Up to seven groups must be searched in a single-entry numerical search manual to identify a phase.

Use of the program NBS*AIDS83 to modify data in the ICDD Powder Diffraction File (PDF) has led to substantial changes in card entries for Sets 1-33, in contrast to the previous policy of the International Centre for Diffraction Data of republishing cards where data has been significantly altered. Further changes to data have been revealed in the use of the database with the Philips PLUS 37 search and retrieval system.

An X-ray analysis method has been developed for the quantitative analysis of pyrite (FeS2) in coals and lignites. Requiring neither the use of external or internal references, the method linearly relates diffraction peak area in the absorption corrected X-ray diffractogram obtained from the finely powdered coal to the pyrite abundance. The [311] diffraction peak of pyrite (FeS2) has been used to develop the analysis protocol. The Argonne premium coals have been used as the experimental subjects. The abundance of pyrite in each coal has been measured from the absorption corrected diffractograms, which has been constructed from the experimentally measured diffraction intensities and the mass absorption coefficient of each coal sample. The accuracy (accessed from the figure-of-merit and the net count uncertainty associated with the 1.63 Å pyrite peak) as well as the lower limit of detection for pyrite in these coals is presented. The role of the mass absorption coefficient in the conversion of the measured intensity to the absorption corrected intensity is discussed.

The temperature dependence of the cell parameters is given for Bi2Mo3O12, Bi2Mo2O9, γ-Bi2MoO6 and γ'-Bi2MoO6, and the volume expansion coefficient is derived. A description is given of a high-temperature diffractometer (HTD) for temperatures up to about 1600°C in controlled atmospheres.

CdTexSe1-xsolid solutions with (x) ranging between zero and one were prepared by solid state diffusion under vacuum and their precise lattice constants and X-ray powder diffraction data were determined. It was found that alloys with 0≤x≤0.4 possess the hexagonal wurtzite structure while those with 0.5≤x≤1.0 have the cubic zincblende structure. The lattice parameters obeyed Vegard's law according to the following formulae

Extrapolated lattice constants were a = 6.066(6) Å for the cubic form of CdSe and a = 4.563(6) Å and c = 7.502 (10) Å for the hexagonal form of CdTe.

Powder X-ray and optical data have been recorded for a sample of exceptionally rare earth-poor eudialyte (Na12(Ca, REE)6(Fe2+,Mn,Mg)3Zr3(Zr,Nb)x[Si9O27−y(OH)y]2[Si3O9]2(C1,F)z, with x = 0. 1–0.9, y = 1–3 and z = 0.7–1.4) from a pegmatitic vein associated with the peralkaline Windy Fork granite in the north–central Alaska range. The eudialyte is uniaxial positive with ω= 1.6062(2), ε= 1.6138 (3) and microprobe analyses indicate that the sum of REE + Yis less than 0.1 weight percent. Refined unit cell dimensions are: a = 14.2572(4), c = 30.1338(27), Dx= 2.67, F30= 128 (0.006, 42), M20= 76. An indexed powder diffraction pattern is given.

A powder X-ray diffraction technique has been developed to quantify the relative amounts of α-carbamazepine (A) and β-carbamazepine (B) when they occur as a mixture. The theoretical basis of this technique was developed in 1948 by Alexander and Klug (Anal. Chem., 20:886-889). The powder X-ray diffraction patterns of A and B revealed that the line with d-spacing of 10.1 Å was unique to A. The ratio of the integrated intensity of the 10.1 Å line in a mixture of A and B, to the intensity of the 10.1 Å line in a sample consisting of only A, was calculated as a function of weight fraction of A in the mixture. These ratios were also experimentally determined, and there was a good agreement between the theoretical and experimental intensity ratios. The particle size of the samples, the sample preparation technique and the experimental conditions were controlled so as to eliminate the major sources of error in powder X-ray diffractometry. In order to minimize preferred orientation of the particles, a sample holder was specially fabricated.

The heterocycle of a functionalized 2-imidazoline, C15N2OH18, was obtained by reaction when 2-bromo, 2-alkenoïc ketone was allowed to react with a monosubstituted benzamidine. The compound presents a R*R* configuration. X-ray powder diffraction data have been obtained from single multifaceted brown crystals prepared at 273 K in benzene with triethylamine as catalyst. Chemical analysis gives a purity better than 99%. This compound crystallizes in the monoclinic space group P21/c [14]. The cell parameters were determined by employing single-crystal diffraction methods (Bragg and precession patterns) and were refined from accurate powder diffractometer data recorded at T = 293 (1) K.

The low temperature modifications of the normal paraffins n-CnH2n+2crystallize in three groups (Broadhurst, 1962). The structure is triclinic for n even, 6 < n < 26 (Muller and Lonsdale, 1948; Nyburg and Luth, 1972); orthorhombic for n odd, 11 < n < 39 (Smith, 1953; Teare, 1959); and monoclinic for n even, 28 < n < 36 (Shearer and Vand, 1956). In all of these structures the hydrocarbon chains are linear and in trans configuration. The chains are parallel to one another, the terminal methyl groups forming the surfaces of lamella which are more or less perpendicular to the chain axis. For n < ca.36, it is apparently the interlamellar interaction between end methyl groups which dictates the symmetry. For longer chains the structure is usually orthorhombic and comparable to the structure of highly crystalline polyethylenes. Chains do not fold (as they undoubtedly do in polyethylenes) unless n is greater than 102 (Bidd and Whiting, 1985; Ungar and Keller, 1986).

The several crystal forms differ in the manner in which the nearest neighbor chains are related to one another. In the triclinic lattices the packing is such that a triclinic sublattice containing one methylene group is evident. In the other modifications the sublattice is orthorhombic and contains four methylene groups. If the overall symmetry is orthorhombic the long chain axes are perpendicular to the interlamellar surface; the x and y translations, perpendicular to the long axis, are common to both cells. If the nearest neighbor chains are displaced by two or four methylene groups along the chain axis, overall monoclinic symmetry results (Sullivan and Weeks (1970)).

Observed and calculated X-ray powder diffraction data are given for cis-[bis (7,9 dimethylhypoxanthine) (ethylene diamine) platinum (II)] dihexafluorophosphate. The paper details how the powder data were obtained with CrKα1radiation and how the quality rating of the pattern was assessed with respect to unique indexing and with regard to the agreement between calculated and observed relative intensities.

X-ray powder diffraction analysis of Diltiazem Hydrochloride C22H26N2O4S·HCl reveals that the compound crystallizes in an orthorhombic unit cell with the powder data unit cell parameters of a=9.08(1), b=42.09(4), c=6.03(1) Å, V=2305 Å3. The unit cell dimensions determined by single crystal diffraction analysis agree well with those of powder diffraction analysis. Samples prepared under different crystallization conditions yielded the same powder patterns.

X-ray powder diffraction and optical data are presented for alkali-deficient schorls from two tourmaline-dumortierite deposits. The compositions of both schorls reflect the presence of an alkali-defect substitution, whereby the alkali cation deficiencies in the crystal structure are charge balanced by trivalent for divalent cation substitutions in the octahedral sites. Refined unit cell and optical data are as follows: a = 15.9523(15), c = 7.1466(2) Å, F30 = 104(0.009, 32), M20= 68, ε = 1.638(2), ω = 1.660(2), Dx= 3.12 for the schorl from Jack Creek, near Basin, Montana, U.S.A. and a = 15.9800 (15), c = 7.1504(2) Å, F30= 156(0.006, 32), M20= 152, ε = 1.642(2), ω = 1.668(2), Dx= 3.17 for the schorl from Ben Lomond, Hervey Range, North Queensland, Australia. Indexed X-ray powder diffraction patterns are also presented.

The influence of grinding procedures on the intensity and full-width-half-maximum for the 101 line of the X-ray powder diffraction pattern for α-quartz has been investigated using samples of controlled grain size. Data collected on powders obtained by four dry grinding methods show substantial variations (up to 35%) in the quartz diffraction intensities. These variations are evident in the <5 μm size fractions and are attributed to the creation of different thickness of amorphous silica layers on quartz grains by grinding. This result suggests that optimum grinding conditions should be defined for quantitative X-ray diffraction analysis.

Powder data for Ag2SO4were obtained with a conventional diffractometer equipped with a vacuum heating chamber. The transition from the low-temperature orthorhombic phase occurs over a temperature range of about 415° to 425°C and forms a hexagonal phase plus metallic silver. The lack of a sharp transition must be taken into account in high-temperature X-ray diffraction or DSC/DTA studies. The lattice parameters of the high-temperature hexagonal phase are a = 5.531(3), c = 7.456(5)Å at 440°C, λ = 1.540562 Å. Crystal structure determination was not completed because of uncertainty in the chemical composition.

Three orthovanadates ATh2(VO4)3with A = Li, Na, Ag have been synthesized by solid state reaction. Single crystals of AgTh2(VO4)3were obtained. This compound is isotypic with sheelite whose space group is I41/a(88). The two other compounds (A = Li, Na) have a zircon type structure: I41/ amd(141). Unit-cell parameters and powder diffraction data for the three compounds are reported.

Barium titanyl oxalate tetrahydrate, Ba(TiO)(C2O4)2.4H2O, has been investigated by means of X-ray powder diffraction. Precise powder diffraction data were obtained by a conventional diffractometer with strictly monochromatic radiation. Unit cell dimensions were determined by an indexing program based on the variation of parameters by successive dichotomies. A monoclinic cell was found, a=14.044(2)Å, b=13.812(2)Å, c=13.382(2)Å, β=91.48(1); V=2594.9Å3, which is characterized by the figures of merit M20=46.5 and F30=107(0.0056, 50). The complete powder pattern was reviewed by means of the program NBS*AIDS83 and the 81 first lines were indexed. Structural imperfections were not detected from the diffraction line widths, which are comparable to the instrumental resolution.

Yttrium oxalate dihydrate, Y2(C2O4)3.2H2O, has been investigated by means of X-ray powder diffraction. Unit cell dimensions were determined by an indexing program based on the variation of parameters by successive dichotomies. The diffractometer data were collected with strictly monochromatic radiation. A monoclinic cell was found: a=9.3811(8)Å, b=11.6385(15)Å, c=5.9726(7)Å, β=96.079(8)°, which is characterized by the figures of merit M20=87 and F30=112 (0.0065,41). A preliminary analysis of the anisotropic line broadening has revealed some microstructural properties. It is shown that line broadening is mainly due to a micro-strain effect.