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An organically templated yttrium fluoride has been prepared hydrothermally and characterised by X-ray powder diffraction. The crystal structure of [C{sub 3}N{sub 2}H{sub 12}]{sub 0.5}[Y{sub 3}F{sub 10}] may be regarded as a 'Super-Diamond' framework, space group Fd3-bar m, a=15.4817(1)A, where each carbon atom site of the diamond structure is replaced by a polyhedral [Y{sub 6}F{sub 8}F{sub 24/2}]{sup 2-} unit. The basic framework type is isostructural with the known phase (H{sub 3}O)[Yb{sub 3}F{sub 10}].H{sub 2}O. The novelty in the present case lies in the use of the organic structure-directing agent 1,3-diaminopropane.

The high temperature behaviour of two forms of sodium yttrium fluoride, i.e. Na1.5Y1.5F6 (hexagonal) and NaYF4 (cubic), have been studied using high temperature X-ray diffraction (HT-XRD) in the temperature range of 293–1073 K in vacuum. The studies revealed that both modifications are stable up to 773 K. The temperature variation of the lattice parameters as well as the coefficients of the average lattice thermal expansion of the compounds have been evaluated in the range 293–773 K. The coefficient of the average volume thermal expansion of NaYF4 (αv=81.68×10-6 K−1) was found to be much higher than that of Na1.5Y1.5F6 (αv=66.25×10−6 K−1). At higher temperatures (>1000 K), Na1.5Y1.5F6 (hexagonal) and NaYF4 (cubic) decompose into a new phase, probably due to loss of NaF. The phase evolution has been identified in situ.