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The solubility of Nd 2 O 3 in NdF 3 -LiF-MgF 2 melts is about 0.08-0.38 mol% when the NdF 3 concentration varies from 15 to 30 mol% at 900 ЊC. The solubility increases from 0.13 mol% at 750 ЊC to 0.22 mol% at 900 ЊC in the NdF 3 -LiF eutectic. When MgF 2 is added to NdF 3 -LiF binary melts saturated with Nd 2 O 3 , the Nd 2 O 3 solubility seems to decrease slightly at 30 mol% NdF 3 , while a slight increase was observed with 15 mol% NdF 3 in the binary. When dissolving Nd 2 O 3 in the NdF 3 -LiF eutectic Raman spectroscopy showed that the complex ions NdOF (x Ϫ 1)Ϫ x and Nd 2 OF (x Ϫ 1)Ϫ x ϩ 3 may form in the melt. The most reasonable candidates seem to be: NdOF 4 3Ϫ and NdOF 5 4Ϫ among the mononuclear compounds and Nd 2 OF 10 6Ϫ , Nd 2 OF 8 4Ϫ among the binuclear complexes. I ANISO (ω) = I HV (ω) (2) DALTON

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Raman spectra of molten ThCl 4 -ACl (A = Li, Na, K or Cs) mixtures have been measured. The complete composition range has been studied for all systems at temperatures up to 960 ЊC. The spectral changes upon melting the binary compounds A 2 ThCl 6 , A 3 ThCl 7 and the pure crystalline ThCl 4 were also measured. The data indicate that in molten mixtures rich in alkali-metal chloride the predominant species are the ThCl 6 2Ϫ octahedra [ν 1 (A 1g ) 297 and ν 5 (F 2g ) 125 cm Ϫ1 ] in equilibrium with the ThCl 7 3Ϫ pentagonal bipyramid. With increasing ThCl 4 mole fraction above 0.3 the frequency of the ν 1 (A 1g ) band increases continuously reaching its maximum (≈340 cm Ϫ1 ) in pure molten ThCl 4 . It appears that in mixtures rich in ThCl 4 edge bridging of thorium() octahedra occurs yielding chain species of the type [Th n Cl 4n ϩ 2 ] 2Ϫ and [Th n Cl 4n Ϫ 2 ] 2ϩ where the end Th atoms of the chain are six-and four-fold co-ordinated for the anion and cation respectively. The known ionic character of these melts suggests that the chain length is rather small and that most probably the species have low n values (e.g. Th 2 Cl 10 2Ϫ , Th 3 Cl 14 2Ϫ, Th 3 Cl 10 2ϩ , . . .). Glassy ThCl 4 was formed by slow cooling of the melt. The vibrational modes and the inferred structure of the glass are similar to those of the melt.