Temperature-induced structural changes in CaCl{sub 2},CaBr{sub 2}, and CrCl{sub 2}: A synchrotron x-ray powder diffraction study

Journal Article · Thu Dec 01 04:00:00 EST 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.72.2· OSTI ID:20787740

Howard, Christopher J; Kennedy, Brendan J; Curfs, Caroline ^[1]

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1. Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, New South Wales 2234 (Australia) and School of Physics, University of Sydney, Sydney, New South Wales 2006 (Australia)

The halides CaCl{sub 2},CaBr{sub 2}, and CrCl{sub 2} all adopt, at room temperature, the same distorted rutile structure, in orthorhombic space group Pnnm, known as the calcium chloride structure. Upon heating, CaCl{sub 2} and CaBr{sub 2} each undergoes a continuous transformation to the true tetragonal rutile structure, in space group P4{sub 2}/mnm, the transition temperatures being 235 and 553 deg. C, respectively. By contrast, the structural change in CrCl{sub 2} upon heating is just further elongation of octahedra already lengthened by Jahn-Teller effects, and no phase transition occurs. The orthorhombic structure is maintained by a strong and temperature-dependent geometrical coupling of the orthorhombic strain to the order parameter, represented by the tilt angle of the CrCl{sub 6} octahedron.

• OSTI ID: 20787740
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 21 Vol. 72; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CALCIUM BROMIDES
CALCIUM CHLORIDES
CHROMIUM CHLORIDES
COUPLING
HEAT TREATMENTS
HEATING
JAHN-TELLER EFFECT
ORDER PARAMETERS
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
RUTILE
STRAINS
STRESSES
TEMPERATURE DEPENDENCE
TETRAGONAL LATTICES
TRANSITION TEMPERATURE
X-RAY DIFFRACTION