The usefulness of an X-ray powder diffraction data base, such as the one published by the International Centre for Diffraction Data, is largely dependent on continued additions of indexed powder patterns of single-phase materials of interest to data-base users. The single-phase character of a specimen is generally established by using known values of the unit cell constants to index all its powder pattern lines.

In this manuscript we describe indexing procedures based on crystal data which provide only relative values of the cell dimensions, rather than the absolute values usually considered to be essential to the indexing process. To the best of our knowledge, the use of such data for indexing powder diffraction patterns has generally been overlooked or ignored by X-ray crystallographers. We refer to the large numbers of goniometric measurements of crystals which have been published both before, and since, the discovery of X-ray diffraction. These provide useful descriptions of chemical and physical properties of crystals as well as measurements of relative dimensions of unit cell axes. The latter are presented in the form of a/b, b/b and c/b, together with the interaxial angle or angles, if the cell is nonorthogonal.

Quantisation of low-quartz in crystalline mixtures has been performed by X-ray powder diffractometry (XRPD) for many years. Conventional methodology, using discrete-peak integrated intensities, is frequently performed employing calibrations prepared with natural low-quartz specimens. Previous research showed that from a conventional XRPD study of low-quartz specimens, the amorphous content of a suite of natural low-quartz specimens ranged from 1% to 28%. That study thereby underlined the importance in XRPD calibration of characterising the amorphous content (or its complementary quantity “weight fraction of crystalline material, WCFM” employed here). This paper describes an application of pattern-fitting Rietveld analysis for characterising the WCFM in a suite of low-quartz specimens. The results gave WCFM values ranging from 0.91 (esd, σ= 0.02) to 1.00(0.02) for six specimens for which the SiO2chemical content ≥ 99.5%.

Don Hanawalt died three years ago this June. To those of us who were privileged to know him he was a special person, a man of boundless energy and tireless enthusiasm. In a very real sense Don was a founder in the use of the powder diffraction as a practical laboratory technique. His pioneering contributions included the universally employed search method which, today, still bears his name, and which really established qualitative phase identification. To Don's chagrin, his work never received the same enthusiastic acceptance among chemists that it did by mineralogists and metallurgists. Several months before Don died, Richard Rose of the Journal Staff interviewed Don with the idea of writing an article for the Journal covering Don's contributions to the field of powder diffraction in general, and his work within the International Centre in particular. Because of Don's untimely demise the work was never completed… but in order that a description of Don's interest and work in the powder diffraction field should be recorded, we have taken the tape transcripts and edited them into what we hope will be a cohesive, if somewhat abbreviated, story. Where possible, we have retained the actual language of the interview. Where necessary, minor corrections have been made to some of the dates mentioned by Don. The interview starts by reviewing the early days of X-ray analysis.

Two methods may be used to measure the reference intensity ratio: (1) by measuring intensities from samples prepared by mixing the analyte and standard together in a known weight ratio and (2) measuring separately the intensities for the analyte peak and reference standard peak from pure phase preparations and by correcting the intensities with mass absorption coefficients. Both methods give identical results that are independent of the difference in mass absorption between analyte and standard. These reference intensity ratios may be universally applied to both matrix flushing and adiabatic procedures in multicomponent analysis providing that preferred orientation, microabsorption, and extinction can be eliminated or greatly minimized in the samples under analysis.

A study has been conducted with gibbsite specimens, on the use of Rietveld X-ray powder diffraction (XRPD) pattern fitting for quantitating preferred orientation in powders. This study has shown that an earlier formula gives results which correlate closely with an empirical measure of morphology proposed recently for gibbsite powders, viz., the ratio of the XRPD intensities for the (002) line and the (110, 200) doublet lines. A method is proposed on the basis of this correlation for the correction for preferred orientation of line intensities in gibbsite powder patterns. The correction method appears to have excellent potential for XRPD quantification of gibbsite levels in mixtures, and could have general application for coping with preferred orientation effects in the quantitation of other phases.

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.

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.

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)).

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.

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.

Cadmium hydroxide nitrate dihydrate, Cd5(OH)8(NO3)2·2H2O, and zinc hydroxide nitrate diammoniac, Zn5(OH)8(NO3)2·2NH3, have been investigated by means of X-ray powder diffraction. Their unit cell dimensions were found by an indexing program and confirmed by single crystal studies. Precise data collected with strictly monochromatic radiation are reported. The figures of merit are F30=118 (0.0071,36) for the cadmium compound and F30=53 (0.015,38) for the zinc compound. A short discussion of the unit cell parameters compared to those of a related zinc hydroxide nitrate dihydrate is presented.

X-ray powder diffraction data for the compound Di-(1-phenylisopropyl)formamide, C19H23NO are reported. The crystals are monoclinic and the space group P21/c, with a = 10.764(2), b = 14.893(2), c = 10.862(2) Å, β= 108.49(1)°, Z = 4, Dx= 1.132, Dm= 1.120(2) gm/cm3.