Abstract
The effect of pressure on the crystal structure of thallium selenate (Tl 2SeO 4) ( Pmcn, Z=4), containing the Tl + cations with electron lone pairs, has been studied with single-crystal X-ray diffraction in a diamond anvil cell up to 3.64 GPa at room temperature. No phase transition has been observed. The compressibility data are fitted by a Murnaghan equation of state with the zero-pressure bulk modulus B 0=29(1) GPa and the unit-cell volume at ambient pressure V 0=529.6(8) Å 3 ( B′=4.00). Tl 2SeO 4 is the least compressible in the c direction, while the pressure-induced changes of the a and b lattice parameters are quite similar. These observations can be explained by different pressure effects on the nine- and 11-fold coordination polyhedra around the two non-equivalent Tl atoms. The SeO 4 2− tetrahedra are not rigid units and become more distorted. Their contribution to the compressibility is small. The effect of pressure on the isotypical oxide materials A 2 TO 4 with the β-K 2SO 4 structure is discussed. It appears that the presence of electron lone pairs on the Tl + cation does not seem to influence the compressibility of Tl 2SeO 4.
Published Version
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