A new mixed lead thorium phosphate, Pb0.5Th2(PO4)3, has been isolated in the system PbO–ThO2–P2O5. Its crystal structure (monoclinic symmetry, a=17.459(1) Å, b=6.8451(4) Å, c=8.1438(5) Å, β=101.247(5)°, space group C2/c) has been determined from conventional monochromatic X-ray powder diffraction data. The structure is related to the MITh2(PO4)3 structure type. Lead atoms are located in the channels parallel to the c axis, out of the twofold axis for 0.97 Å, and are statistically distributed on a quarter of crystallographic positions. The thermal stability of this material is greater than that of the monazite-type compound PbTh(PO4)2.

Powder X-ray diffraction data for Ba12Cl5F19 are reported. The cell is hexagonal (space group P6¯2m, Z=1), with a=14.0856(3) Å and c=4.2733(2) Å.

A new phase in the system BaO–MnO–SiO2 obtained by a pyrosynthetic method has been inves- tigated using electron microprobe analysis (EPMA), X-ray powder diffraction (PDA), and trans- mission electron diffraction. The lattice parameters and possible space group of the phase with a general composition BaMnSi2O6 were determined as follows: a=13.896, b=12.261, c=10.781 Å, β=103.47°, space group P21/m, Z=12.

X-ray powder diffraction data for κ-Al2O3 are reported. It was concluded that κ-Al2O3 belongs to the orthorhombic crystal system with space group Pna21. The lattice parameters were found to be a=4.8351(3) Å, b=8.3109(5) Å, c=8.9363(3) Å. There are 16 Al3+ and 24 O2− in the unit cell, and thus the number of chemical formulas in the unit cell, Z, is 8. The volume V of the unit cell is equal to 359.09(6) Å3 and the theoretical density Dx is 3.772 g/cm3. The Smith–Snyder (F20) and the de Wolff (M20) values for these data are 136.1 (0.0059, 25) and 98.4, respectively.

Powder diffraction data for semiconductor and metallic states of vanadium dioxide are presented. The structures are refined by Rietveld methods using a monoclinic cell (a = 5.7529Å, b = 4.5263Å, c = 5.3825Å, β = 122.61°) and space group P21/c for the room temperature data, and a tetragonal cell (a =4.5540Å, c = 2.8557Å) and space group P42/mnm for data collected at 400 K. The similarity between the corresponding X-ray diffraction patterns is discussed. The transition process from the monoclinic to tetragonal phase is investigated and initial evidence for the coexistence of phases over a small temperature range is presented.

The crystal structure of the low-temperature oxidized form of Sr49.5Ca16.5Bi34O151 has been determined using a combination of neutron, synchrotron, and laboratory X-ray powder diffraction data. The structure is pseudo-orthorhombic; systematic absences and successful refinement indicated the true structure to be monoclinic, with space group P2l/n. Structural refinement using only neutron powder data yielded the lattice parameters a=8.38 898(29) Å, b=5.99 334(21) Å, c=5.89 586(20) Å, β=89.997(8)°, and V=296.43(3) Å3. This compound is a distorted perovskite phase [described in the perovskite ABO3 formula as Sr(Bi0.7Ca0.3)O3] with ordering of the M-site cations, resulting in the formula A2MM′O6. In this ordered structure, the A sites are solely occupied by Sr, the M sites mainly by Bi, while on the M′ sites Bi and Ca are distributed in an approximate ratio of 2:3. The MO6 and M′O6 octahedra share corners, and are tilted with respect to the neighboring layers with an angle of ∼15° around all three axes. The tilt system symbol is a+a−a− according to Glazer notation. All Bi ions are in the 5+ oxidation state.

The two germanates K2MgGeO4 and K2CdGeO4 have been synthesized by solid-state reaction. These compounds are isostructural with K2ZnGeO4, space group Pca21 (No. 29), Z=8. Unit cell parameters were determined: for K2MgGeO4a=11.1810(11), b=5.5708(6), c=15.8694(16) Å, V=988.5(3) Å3 and for K2CdGeO4a=11.4777(24), b=5.7155(7), c=16.1732(17) Å, V=1061.0(5) Å3. Powder diffraction data are reported.

I had just completed my BS in chemistry at Northwestern University in 1928 and had passed the Civil Service Chemistry Examination, and my fiance had passed an examination for the Civil Service Commission and had been offered a job at that agency in Washington. So we got on a train and came to DC, arriving 15 March 1928. I went to the Civil Service Commission (now called the Office of Personnel Management) and was directed to NBS where there were a number of openings for a P1 chemist. There I talked to Dr. Wichers in Chemistry and to J. Murray in the Lime and Gypsum Section. I took a job in the latter. On 31 March, we got married and on Monday, 2 April 1928, I started work in the Lime and Gypsum Section of the Clay and Mineral Products Division.

Highly uniform fine powder sample layers may be prepared for X-ray diffractometry by aerosol suspension and collection on glass fiber filter substrates. A tubular aerosol suspension chamber (TASC) has been fabricated for this purpose. Essential components include a 500 ml gas buret, 4.7-cm filter cassette, rotameter, and rotary pump. Aerosol particles are generated within the TASC buret by convection within a fluidized bed of glass beads mixed with the sample. Exceptional uniformity of load and randomness of particle orientation has been demonstrated for samples prepared with this system. For quantitative analytical work accurate intensities may be obtained using corrections to raw intensities based on fundamental sample and filter properties.

The crystal structure of metastable Li2Si2O5, Fw = 150.05, has been refined by the Rietveld method using high resolution X-ray powder diffraction data recorded at the Daresbury Synchrotron Radiation Source on the new 8.3 diffractometer. Li2Si2O5, in keeping with many compounds of interest to the materials scientist, exhibits relatively broad diffraction peaks. It is important to establish the quality of crystal structure data that may be obtained from such materials on this new instrument. Various functions were used to model the peak shape from this instrument; a split-Pearson VII function appeared to be marginally superior to Pearson VII or Pseudo-Voigt functions. Refinement was carried out using the split-Pearson VII in the space group Pbcn (60) and terminated with a = 5.6871(6), b = 4.7846(5), c = 14.645(1) Å, V = 398.50 Å3, Z=4, Dc= 2.502 gcm−3, Rwp = 17.06, Rex = 14.48 and Χ2 = 1.39. The refined parameters are compared with those obtained from a previous single crystal X-ray determination.

X-ray powder data originally published for innelite—Na2Ba3(Ba, K, Mn)(Ca, Na)Ti(TiO2)2[Si2O7]2(SO4)2—were erroneously those of catapleiite. The new data reported here are compared with powder data calculated from the published structure. The cell is triclinic (space group P1, Z=1), a=14.71(1) Å, b=7.115(7) Å, c=5.379(4) Å, α=90.02(7)°, β=94.68(8)°, γ=98.43(9)°, V=555.0(6) Å3, F30=5.2(0.053,109).

An algorithm has been derived, forming the basis of a computer program called BBCCURV, which calculates a Bragg-Brentano X-ray diffractometer intensity correction curve (intensity correction factor Kivs. 2θi) given the diffractometer and sample dimensions, and the effective (not theoretical) linear absorption coefficient of the sample. Use of this calibration curve gives a set of intensity data free from aberrations, which are caused mainly by sample transparency, curvature of the diffraction cones passing through the receiving slit and possible beam overflow past the specimen at low angles.

The algorithm was confirmed with a full-profile Rietveld refinement of Bragg-Brentano X-ray diffraction data from a H+-ZSM5 zeolite sample. On introducing a BBCCURV correction curve, the profile R-factor over the pattern points dropped from 30.8% to 16.5%, a significantly better fit when the data were corrected with a BBCCURV curve.

BBCCURV intensity calibration curves from LiF (μ= 1.5 mm−1) through zeolites, clays, ZnO, rutile, Pb(NO3)2and finally solid metal (μ= 1000 mm−1) (CoKα) indicate upward revision of the measured diffractometer intensities by factors of between 2 and 10 at 2θ= 5° for these sample types, normalised to a correction factor of 1.0 at 2θ= 44°. Corrections of this magnitude to Bragg-Brentano data are thus significant in full-profile structure refinement and quantitative analysis with Bragg-Brentano data. Use of a variable divergence slit (VDS) is not appropriate in full-profile refinements as the intensity aberrations are magnified, and conversion from VDS data to aberration-free data is sample- and transparency-dependent, and not the simple area (sinθ)−1function generally assumed. Use of a fixed divergence slit with a BBCCURV-type calibration is recommended.

Results are given of an assessment of a Rietveld-type X-ray powder diffraction pattern fitting structure refinement technique for assaying powdered mixtures as an alternative to conventional discrete peak empirical methods of the type described by Klug and Alexander (1974) and Chung (1974). The values obtained for a mixture of corundum and α-quartz, following calibration of the instrument with a profile of the former, indicate that this technique has excellent potential as an analytical tool.