Crystal-Chemical Characteristics of Silicon−Neodymium Substituted Hydroxyapatites Studied by Combined X-ray and Neutron Powder Diffraction

AbstractSingle crystals and powder samples of Ca2Bi5O5and Ca4Bi6O13have been synthesized and studied using single crystal X-ray diffraction as well as X-ray and neutron powder diffraction. Unit cell dimensions were calculated using a least squares analysis that refined to a δ2θof no more than 0.03°. A triclinic cell was found with space group , a = 10.1222(7), b = 10.1466(6), c = 10.4833(7) Å. α= 116.912(5), β= 107.135(6) and γ= 92.939(6)°, Z = 6 for the Ca2Bi2O5compound. An orthorhombic cell was found with space group C2mm, a = 17.3795(5), b = 5.9419(2) and c = 7.2306(2) Å, Z = 2 for the Ca4Bi6O13compound.

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Probing Octahedral Tilting in Dion-Jacobson Layered Perovskites With Neutron Powder Diffraction and Raman Spectroscopy

MRS Proceedings ◽

10.1557/proc-988-0988-qq08-06 ◽

2006 ◽

Vol 988 ◽

Author(s):

Joshu A. Kurzman ◽

Margret J. Geselbracht

Keyword(s):

Raman Spectroscopy ◽

Powder Diffraction ◽

Neutron Powder Diffraction ◽

Layered Perovskite ◽

Strontium Content ◽

Solid Solution Formation ◽

X Ray ◽

Unit Cells ◽

Octahedral Tilting ◽

Average Size

AbstractTwo new Dion-Jacobson type layered perovskite solid solutions, RbCa2-xSrxM3O10 (M = Nb, Ta; 0 ≤ x ≤ 2), were prepared and studied by X-ray powder diffraction, neutron powder diffraction, and Raman spectroscopy. X-ray powder diffraction confirmed single-phase solid solution formation with continuous expansion of the idealized primitive tetragonal unit cell with increasing strontium content. Neutron powder diffraction studies of selected samples revealed lower symmetries and larger unit cells, as necessitated by octahedral tilting within the perovskite slabs, compared to the idealized primitive cell. As the average size of the A-cation in the perovskite slab is varied from Sr2+ to Ca2+, more extensive octahedral tilting is introduced. Vibrational modes of the perovskite slab observed using Raman spectroscopy show subtle changes as a function of calcium/strontium content and more intriguing differences between the isostructural niobates and tantalates.

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Synthesis and structural characterization of Ca12Ga14O33

Scientific Reports ◽

10.1038/s41598-020-73311-w ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Sabrina E. A. McCoy ◽

John R. Salasin ◽

S. Michelle Everett ◽

Claudia J. Rawn

Keyword(s):

Powder Diffraction ◽

Structural Model ◽

Electronic Band Structure ◽

Rietveld Method ◽

Experimental Studies ◽

Phase Evolution ◽

Neutron Powder Diffraction ◽

Electronic Band ◽

Wet Chemistry ◽

X Ray

Abstract Ca12Ga14O33 was successfully synthesized using a wet chemistry technique to promote the homogenous mixing of the Ca and Ga cations. Rietveld refinements on X-ray and neutron powder diffraction data confirm that the compound is isostructural to Ca12Al14O33, however, with a significantly larger lattice parameter allowing for the cages that result from the framework arrangement to expand. In naturally occurring Ca12Al14O33, the mineral mayenite, these cages are occupied by O2− anions, however, experimental studies exchanging the O2− anions with other anions has led to a host of applications, depending on the caged anion. The functional nature of the structure, where framework distortions coupled with cage occupants, are correlated to electronic band structure and modifications to the framework could lead to interesting physical properties. The phase evolution was tracked using thermogravimetric analysis and high temperature X-ray diffraction and showed a lower formation temperature for the Ca12Ga14O33 analogue compared to Ca12Al14O33 synthesized using the same wet chemistry technique. Analyzing both X-ray and neutron powder diffraction using the Rietveld method with two different starting models results in one structural model, with one Ca position and the caged O on a 24d special position, being preferred.

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