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Notes: A Be-walled conduction cooling He(l) cryostat intended for the interval 20–80 K and the κ geometry of the CAD4 X-ray diffractometer is described. Three-dimensional X-ray intensity data can be collected in the interval − 45 〈 χ 〈 45° with the temperature stability maintained within ± 1 K. The experimental problems caused by centering an unseen crystal and by the absorption and scattering in the Be walls are discussed. D(+)-tartaric acid, C4H6O6, was chosen as a test compound. Only minor differences occur in its crystal and molecular geometry between 295 and 35 K.

Notes: A powder diffractometer (CPS120 by INEL) equipped with a position-sensitive detector covering 120° in 2θ has been tested and the data have been successfully used with the Rietveld method. The detector was found to have a characteristic variation in linearity of ±1.5%. A calibration compound with well known 2θ values was used to determine a cubic spline calibration function to describe the 2θ versus channel-number function, which was then incorporated in the Rietveld analysis program. A procedure is also described to correct for air and capillary scattering, taking sample absorption into account. The methods have been applied to a structure refinement of quartz and to a study of the dehydration process of the zeolite thomsonite. Quartz: Rp = 11.0%, Rw = 14.0% and RB = 7.9%, based on 10 〈 2θ 〈 116.3° in 3470 steps, λ = 1.540598 Å. Space group P312, Z = 3, a = 4.91201 (7), c = 5.40301 (5) Å, x(Si) = 0.4702 (3), Bave(Si) = 0.77 (6) Å2, x(O) = 0.4112 (6), y(O) = 0.2712 (5), z(O) = −0.2811 (4) and Bave(O) = 1.0 (1) Å2. Thomsonite: Rp = 8.18%, Rw = 11.04% and RB = 3.33%, based on 10 〈 2θ 〈 110° in 3270 steps. Space group Pncn, Z = 4, a = 13.0778 (3), b = 13.0398 (3) and c = 13.1970 (3) Å. The unit cell changes continuously with increasing dehydration temperatures up to 523 K, at which a = 12.9725 (3), b = 12.9537 (3) and c = 13.2288 (3) Å. In this first dehydration step, the W3 and W4 molecules coordinated to the Ca/Na site are lost and the Ca/Na and W1 sites are shifted approximately 0.3 Å from their original positions towards the framework O atoms. After dehydration at 573 K, the mode of unit-cell variations is changed: a = 12.908 (3), b = 13.039 (3) and c = 13.034 (3) Å. In this dehydration step, W1 is lost. The W2 site appears unaffected by the dehydration below 573 K. On dehydration above 573 K, the diffraction intensities decrease as the compound becomes amorphous.

Notes: The high intensity of an X-ray synchrotron source in combination with a curved position-sensitive detector covering 120° (CPS120 by INEL) has been used to collect complete powder diffraction patterns, suitable for Rietveld analyses, within minutes. From consecutive patterns (ΔT ∼ 5 K), detailed information was obtained on water expulsion and phase transitions induced by dehydration of the natural zeolites scolecite and mesolite. Scolecite, Ca8Al16Si24O80.24H2O, shows an initial gradual loss of half O(2W). At 4̃80 K, scolecite goes through a phase transition already described by Rinne [Neues Jahrb. Mineral. Beil. (1923). 48, 240–249]. The crystal symmetry changes from F1d1 to Fd11 when half the Ca ions move by 1̃/2c and the remaining O(2W) is expelled. Metascolecite: Ca8Al16Si24O80.16H2O, Fd11, Z = 1, T = 489 K, a = 18.1465 (7), b = 18.8604 (7), c = 6.5396 (3) Å, α = 88.986 (2)°, Rp = 5.42%, RB = 2.51% from 3620 observations, 802 Bragg reflections and 79 refined parameters. Continued heating to 615 K did not further reduce the water content. The dehydration process in mesolite starts with a loss of half the same Ca-coordinated water as in scolecite. The initial water loss is followed by an order/disorder transition, where the Na and Ca ions become randomly distributed over the cation sites. Consequently, the b axis of metamesolite is reduced to 1/3 of bmes and the k ≠ 3n reflections disappear. Metamesolite is very similar to natrolite, with equal numbers of Na atoms, Ca atoms and vacancies in the natrolite Na-atom site and with n(H2O) varying between 16 and 10.67. Metamesolite: Ca5.33Na5.33Al16Si24O80.n(H2O), Fdd2, Z = 1, n(H2O) = 10.6 (2), T = 582 K, a = 18.1039 (6), b = 18.5763 (6), c = 6.5589 (2) Å, Rp = 4.85%, RB = 2.01% from 3620 observations, 424 Bragg reflections and 54 refined parameters. Both scolecite and mesolite have one AlO4 tetrahedron with only one O atom coordinated by a cation. The initially expelled waters are in both cases hydrogen bonded to an O atom in those AlO4 tetrahedra. The initial water expulsions thus worsen the underbonding and trigger the cation rearrangements. The resulting cation distributions in metascolecite and metamesolite are the most even with respect to the AlO4 tetrahedra and are considered the driving force of both phase transitions. The cation rearrangement in mesolite requires cross-channel diffusion and is considerably slower than the in-channel rearrangement taking place in scolecite. In both zeolites, the lower limit in the calcium coordination number was found to be six. The ICDD Powder Diffraction File Nos. are: 45-1489 for Ca8Al16Si24O80.16H2O; 45-1490 for Ca8Al16Si24O80.18.9H2O; 45-1491 for Ca5.33Na5.33Al16Si24O80.12.8H2O; 45-1492 for Ca5.33Na5.33Al16Si24O80.16.7H2O.

Notes: Single crystals of caesium titanyl arsenate (CTA, CsTiOAsO4), with space group Pna21 and isomorphous with potassium titanyl phosphate (KTP, KTiOPO4), have been studied using high-resolution synchrotron X-rays. During the experiments, an electric field was applied along the polar axis [001]. Single-crystal plates, between 300 and 450 μm thick along [001], were polarized by a variable square wave of frequency 20 Hz alternately applied to each side of the plate. A field-induced splitting of the + /− peaks for reflections hkl with l ≠ 0 was observed. This splitting provides information about the coercive field, polarizability and the piezoelectric strain tensor. Two of the piezoelectric coefficients of CTA could be estimated as d31 ∼ 1 and d33 ∼ 27 pm V−1. Whereas the coercive fields were estimated at 2300 V mm−1, the field necessary to reverse the domains just once in CTA was found to be either 560 or 1550 V mm−1, depending on the polarity of the reversed domain in relation to the polarity of the nonswitched part of the crystal.