γ Na2BeF4, its crystal structure at 25° and 74°C and its anisotropic thermal expansion
Abstract
The thermal expansion of γ Na2FeF4 was measured up to 140°C using a Guinier-Lenné camera. Refinement of the crystal structure at 25° and 74°C indicates a temperature dependence of the U's not in agreement with the expansion data. However, consideration of the changes in bond lengths at 25° and 74°C and of the values of the root-mean-squared amplitudes allows a qualitative understanding of the phenomenon. The higher value of the root-mean-squared amplitudes along c positively fix the latter as a preferential direction of stress relief upon heating. Expansion along b is controlled by the rigidity of the M(1) polyhedra located at inversion centers and opposing cooperative phenomena of translational motion along this direction. Due to the stability of the tetrahedral configuration controlling the a repeat, expansion along a is the smallest one, in agreement with theoretical expectations. The abrupt increase in α1 at 120°C is attributed to the formation of a stronger repulsion potential caused by a change from a sp3 configuration of the tetrahedral bonds to one tending toward lower values of orbital hybridization. This process opposes the close-packed arrangement and at a critical temperature a phase change is expected to take place. This is in agreement with the experimental data since at 187 ± 5°C an inversion to a monoclinic phase was positively identified.
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- Some conditional distributions of the structure factors and related conditional expectation values
- γ Na2BeF4, its crystal structure at 25° and 74°C and its anisotropic thermal expansion
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- Die Kristallstruktur von Strontiumnitrat-Tetrahydrat, Sr(NO3)2 · 4H2O
- Bemerkungen zur Geschichte der Raumgruppen-Symbole von Fedorow, Schoenflies und Hermann-Mauguin*
- Structure refinement of anthrone, C14H10O
Articles in the same Issue
- Some conditional distributions of the structure factors and related conditional expectation values
- γ Na2BeF4, its crystal structure at 25° and 74°C and its anisotropic thermal expansion
- Crystal structure and hydrogen bonding of copiapite
- The crystal and molecular structure of 4,8,9,10-tetrachloro-2,6-dithiaadamantane, C8H8Cl4S2*
- Wirkungsbereichstypen einer verzerrten Diamantkonfiguration mit Kugelpackungscharakter
- The application of the partial Patterson method and the thirteenfold hexagonal superstructure of Cu7As6Se13
- The investigation of superstructures by means of partial Patterson functions
- Die Kristallstruktur von Strontiumnitrat-Tetrahydrat, Sr(NO3)2 · 4H2O
- Bemerkungen zur Geschichte der Raumgruppen-Symbole von Fedorow, Schoenflies und Hermann-Mauguin*
- Structure refinement of anthrone, C14H10O
