scholarly journals Experimental Determination of Scan-truncation Losses from Low-temperature (16 K) Single-crystal X-ray Measurements

1988 ◽  
Vol 41 (3) ◽  
pp. 503 ◽  
Author(s):  
Riccardo Destro
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
Experimental Determination ◽  
Least Squares ◽  
Spectral Distribution ◽  
Experimental Measurements ◽  
Fourier Methods ◽  
X Ray ◽  
Least Squares Fitting

Model intensity profiles have been obtained for biscarbonyl[ 14]annulene by convoluting the Mo Ka spectral distribution with two functions derived from experimental measurements at 16(1) K, up to 26Mo = 110�, of a spherical crystal mounted on a four-circle diffractometer equipped with the Samson low-temperature apparatus. The process includes accurate measurement of the inherent background, treatment of the profiles by numerical Fourier methods, and least-squares fitting. Owing to the instrumental configuration of the diffractometer used in this investigation, the first step of the process has required a careful determination of the X dependence of the background, besides the usual 26 dependence. Truncation losses for the crystal under study, evaluated for several scan ranges, are far larger than usually assumed or predicted.

Space-Group Determination of the Orthorhombic Form of NaV6O11

1995 ◽  
Vol 28 (5) ◽  
pp. 599-603 ◽  
Author(s):  
Y. Kanke ◽  
H. Shigematsu ◽  
K. Ohshima ◽  
K. Kato
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Single Crystal ◽  
Diffraction Study ◽  
Structural Phase ◽  
Unit Cell ◽  
Single Crystal Diffraction ◽  
Space Group ◽  
X Ray

The unit cell and space group of orthorhombic NaV6O11 (low-temperature form) are found by an X-ray single-crystal diffraction study at 300 K (hexagonal, P63/mmc), 100 K (hexagonal, P63 mc) and 20 K (orthorhombic). The orthorhombic form (o) shows no superstructure and its unit cell is related to the hexagonal one (h): a o ≃ a h + b h , a o ≃ −a h + b h and c o ≃ c h . Bijvoet-pair examination confirms that it crystallizes in the noncentrosymmetric space group Cmc21. The hexagonal (P63 mc)-orthorhombic (Cmc21) structural phase transition is proved to be of second order.

An X-ray determination of the thermal expansion of the intermetallic compound Ni3Zr

1983 ◽  
Vol 16 (6) ◽  
pp. 645-646 ◽  
Author(s):  
S. K. Shadangi ◽  
S. C. Panda ◽  
S. Bhan
Keyword(s):  
Thermal Expansion ◽  
Intermetallic Compound ◽  
Least Squares ◽  
Temperature Interval ◽  
X Ray ◽  
Least Squares Fitting ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Ray Methods

The lattice spacings of the intermetallic compound Ni3Zr have been measured by X-ray methods in the temperature interval 298–1033 K using a Debye–Scherrer camera. In all the cases the measured lattice spacings have been found to increase non-linearly with temperature and the dependence has been expressed by a polynomial of second degree from the least-squares fitting of the data. The thermal expansion coefficients for both parameters have been found to decrease with increase in temperature.

scholarly journals Low Temperature Crystal Structure of Natural Diosgenone

2002 ◽  
Vol 57 (9-10) ◽  
pp. 947-950 ◽  
Author(s):  
Oscar E. Piro ◽  
Eduardo E. Castellano ◽  
Gloria E. Tobón Zapata ◽  
Silvia Blair Trujillo ◽  
Enrique J. Baran
Keyword(s):  
Molecular Structure ◽  
Crystal Structure ◽  
Low Temperature ◽  
Single Crystal ◽  
Least Squares ◽  
Monoclinic Space Group ◽  
Steroidal Sapogenin ◽  
Full Matrix ◽  
X Ray ◽  
Low Temperature Crystal Structure

The molecular structure of diosgenone, a natural steroidal sapogenin, closely related to diosgenin and isolated from Solanum nudum, was solved by single crystal X-ray diffractometry at 120 K and refined by full-matrix least-squares to an agreement factor, R1 = 0.054. It crystallizes in the monoclinic space group P21, with a = 15.1870(4) Å , b = 7.2710(2) Å , c = 21.2840(6) Å , β= 99.251(1) °, and four molecules in the unit cell (Z = 4). The results constitute the first structural report on a steroidal sapogenin from the diosgenin group.

Lewis-Base Adducts of Group 1B Metal(I) Compounds. XXII. Crystal Structure of 'Bis(pyridine)silver(I) Perchlorate

1985 ◽  
Vol 38 (9) ◽  
pp. 1325 ◽  
Author(s):  
JC Dyason ◽  
PC Healy ◽  
LM Engelhardt ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Least Squares ◽  
Complex Cation ◽  
Lewis Base ◽  
X Ray ◽  
Ray Methods

Determination of the crystal structure of 'bis (pyridine)silver(I) perchlorate' by single-crystal X-ray methods shows it to be of 2.4:1 pyridine:silver (I) perchlorate stoichiometry , the structure being refined by least squares to a residual of 0.054 for 1142 'observed' reflections. Crystals are tetragonal, I4, a 21.95(1), c 7.684(3) Ǻ. The structure comprises perchlorate anions of two types of I and 4 symmetry, together with two types of complex cation: [Ag( py )2]+, with 1 symmetry, and [Ag( py )4]+ with 4 symmetry. For the two types of cation Ag-N are 2.15(1), 2.16(1) and 2.30(1) Ǻ.

scholarly journals Evaluation of uncertainty in the energy dispersive X-ray fluorescence determination of platinum in alumina

2015 ◽  
Vol 7 (12) ◽  
pp. 5345-5351 ◽  
Author(s):  
P. S. Remya Devi ◽  
A. C. Trupti ◽  
A. Nicy ◽  
A. A. Dalvi ◽  
K. K. Swain ◽  
...  
Keyword(s):  
Least Squares ◽  
Energy Dispersive ◽  
Weighted Regression ◽  
Calibration Function ◽  
X Ray ◽  
Least Squares Fitting ◽  
Fluorescence Determination ◽  
Analytical Result ◽  
Fitting In

Uncertainty, the most important characteristic of an analytical result, has been evaluated using a bottom-up approach during EDXRF determination of Pt in alumina. The calibration function of the EDXRF spectrometer was derived through bivariate least squares fitting, in combination with weighted regression of the residuals.

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