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Growth of K₅Li₂NdF₁₀ and K₅Li₂PrF₁₀ crystals by the Bridgman method

Piotr Solarz

Polish Academy of Sciences, Institute of Low Temperature and Structure Research (INTiBS), Okólna 2, Wrocław 50-422, Poland

Abstract

The growth of congruently melting K₅Li₂NdF₁₀ and K₅Li₂PrF₁₀ (KLLF) crystals by the Bridgman method is reported. The structure of these crystals are orthorhombic, with the space group Pnma. The unit-cell parameters are a = 2.0775 nm, b = 0.7822 nm and c = 0.6963 for the K₅Li₂LaF₁₀ crystal and they change a little upon submissions of other lanthanide in the series from La to Gd [1]. The crystal structure is built from layers perpendicular to the a axis, formed by LnF₈ dodecahedra and LiF₄ tetrahedra. Lanthanide and lithium ions occupy sites with point symmetry C_s whereas potassium and fluorine ions occupy sites with C_s and C₁ symmetry. The polyhedra do not share fluorine ions and the closest lanthanide ion are separated by about 0.65 nm. Owning these features, exchange interactions between Ln ions maybe neglected. Based on the crystallographic structure, there is only one site for the lanthanide ions.

A stoichiometric mixture of appropriate LiF, KF, NdF₃ and PrF₃ was preliminary heated at about 500 K for 2 hours at vacuum conditions to remove traces of water. Then it was heated up to 1100 K for at least 2.5 hours, under Ar atmosphere, to accomplish the reaction. Finally the single crystal of KLLF were grown by the Bridgman one-zone method in the following conditions: the melt temperature 900 K, temperature gradient 120 K/cm, pulling rate 1 mm/h. For crystal growth the IG-110 graphite were used which gives also the possibility to remove traces of oxygen.

[1] P. Solarz and W. Ryba-Romanowski, Phys. Rev. B 72 (2005) 075105

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