A neutron powder diffraction study of the β to γ phase transformation in NaFeO2
Abstract
The β (low temperature, Pn21a) to γ (high temperature I, P41212) phase transformation in NaFeO2 has been studied by Rietveld analysis of neutron powder diffraction data collected over the temperature range 298 to 1373 K. The results are consistent with a mechanism that involves cooperative rotation of FeO4 tetrahedra in the cristobalite-related tetrahedral framework. The sodium atoms occupy tetrahedral sites in the framework cavities in both structures. The transformation involves a relocation of the framework oxygen atoms around the sodium atoms to change the articulation between NaO4 and FeO4 from corner to edge sharing. The driving force for the transformation appears to be strain, arising from incompatibility between an expanding cavity volume and the bond valence requirements of the sodium atoms in the β phase. The transformation to the γ form allows an increase in the Fe – O – Fe bridging angle to occur while at the same time permitting the volume of the NaO4 tetrahedron to decrease. The number of nearest neighbour Na – Fe distances decreases from 8 in the β phase to 7 in the γ phase.
Diffraction data were collected for two successive traverses of the transition temperature to study a “emory effect” which is manifested as a lower recorded transition temperature for the second traverse. The origin of the effect was interpreted from the structure analysis results as a retention of uncorrelated domains of the γ phase within the β phase on cooling.
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Articles in the same Issue
- The solid phases of deuterium sulphide by powder neutron diffraction
- Crystal and molecular structure of a manganese complex of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA): Mn4(CDTA)2(H2O)9(CH3COCH3)0.5 · Evidence for a Mn7(CDTA)4(H2O)8 unit
- X-ray and electron microscopic determination of Debye characteristic temperature, stacking fault energy and other microstructural parameters in zinc telluride films
- A simple formula for the morphological axial ratio and for indexing
- A neutron powder diffraction study of the β to γ phase transformation in NaFeO2
- Neutron diffraction study of Sr(BrO3)2 · H2O: Statistical tests of intensity variances, refinement including weak and negative intensities
- Crystal structure of N-(1-ethylcarbamoyl-tetrazol-5-yl)-O-(4-tolyl)-isourea
- Analysis of the distribution of impurities in crystals by anomalous X-ray scattering
- Crystal structure and spectra of Trichloro-p-chlorobenzoyl-2-furaldehydohydrazono bismuth(III)
- Polarity determination in (001)-oriented AIII – Bv compound semiconductors by the Kossel technique and chemical etching
- Crystal and molecular structure of 3-nitro-4-hydroxy-phenylalanine nitrate
- The crystal structure of lintisite, Na3LiTi2[Si2O6]2O2 · 2H2O, a new titanosilicate from Lovozero (USSR)
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