Abstract
Powder x-ray-diffraction experiments have been performed on 2H-${\mathrm{CsCdBr}}_{3}$ at room temperature up to 20 GPa. Although this compound is usually considered as quasiunidimensional, such a characteristic could not be evidenced for its elastic bulk properties under pressure. No phase transformation occurs in this pressure range, and the a and c lattice parameters steadily decrease with pressure; their ratio lowers by only 2%. As for the bulk modulus, its first and second pressure derivatives have been calculated using Birch's equation of state. The bulk modulus is low (21.3 GPa) and is in good agreement with the bulk-modulus--volume systematics for usual ionic compounds. The value of the first pressure derivative is also typical of ionic compounds. Above 5 GPa increasing intensities of a few diffraction lines were observed; they are consistent with a shift of the bromine anions inside the cell that leaves the structure unchanged. This is also supported by the variations of the Raman frequencies with volume.
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