Inorganic fluoride crystals are of particular interest to researchers as promising optical materials. In addition, they may be considered as a host matrix for rare earth ions. SrMgF₄ crystals have been attracted attention recently. They were theoretically supposed to have ferroelectricity [1], but still there are no practical proofs. The goal of this work was to grow SrMgF₄ crystals of a good quality, to study their crystal structure and physical properties to check the presence of ferroelectric nature.
SrMgF₄ crystals were grown via vertical Bridgman method. Powders of MgF₂(99.99%) and SrF₂(99.99%) were used as starting materials. To remove oxygenic impurities, adsorbed from the atmosphere, the synthesized mixture was ignited at 1000˚С and the vacuum of 10^-1 Pa in 24 hours. Then the purified material was melted and held stirring up during an hour. The crystals of SrMgF₄ were grown in a two-zone furnace with a temperature in a hot zone of 1200˚С. The pulling speed and the temperature gradient in a growth region were 1 mm/h and 10-20˚C/cm, respectively. The size of grown crystals was 10×10×5 mm.
To study the structure of grown crystals single crystal and powder X-ray analyses were carried out. SrMgF₄ has noncentrosymmetrical monoclinic structure, space group P2₁. All crystallographic parameters were determined. Coordination numbers of Sr ions were estimated. Altogether the structure can be described as a laminated one. Layers, oriented along c axis, are composed of chains, which are drawn along b axis and consist of irregular corner-sharing MgF₆ octahedra, rotated relative to each other (Fig.1). Obtained results are in good agreement with those published earlier [2].
Emission, excitation and reflection spectra were obtained. The value of E_g was estimated and spectroscopic features were studied carefully.
Polarization-optical study showed the presence of phase transition at 170-200ºC. Also pyroelectric properties were detected at nearly the same temperature region. To assign the high-temperature phase powder X-Ray diffraction at the temperature of 300ºC was performed.
According to obtained results SrMgF₄ crystals are promising nonlinear material indeed and more detailed study should be carried out.

[1] S.C. Abrahams, Acta Crystallogr. B58 (2002) 34.
[2] N. Ishizawa, K. Suda, B. Etschmann, T. Oya, N. Kodama, Acta Crystallogr. C57 (2001) 784.

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