FT±IR and Raman spectra of Gd phosphate crystals and glasses D. Ilieva a, * ,B.Jivov b , D. Kovacheva c , Ts. Tsacheva a , Y. Dimitriev b , G. Bogachev d , Ch. Petkov e a Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 11, So®a 1113, Bulgaria b University of Chemical Technology and Metallurgy, 8 Kl. Ohridski Blvd., So®a 1756, Bulgaria c Institute of Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 11, So®a 1113, Bulgaria d Department of Physics, University of So®a, 5 J. Bourchier Blvd., So®a 1164, Bulgaria e Institute of Organic Chemistry, Bulgarian Academy of Sciences Acad. G. Bonchev Str., Bl. 3, So®a 1113, Bulgaria Abstract IR and Raman spectra of xGd 2 O 3 1  xP 2 O 5 glasses x  0:22±0:31 are reported with emphasis on glassy GdPO 3  3 andthecrystallineformsemerginguponitsdevitri®cation.IncreasingtheconcentrationofGd 2 O 3 from0.22 to 0.26 mole fractions leads to an abrupt lowering of the highest observed P±O stretching frequency of 25 cm 1 .The spectral shift is related to changes in both the coordination of the lanthanide ion and the increase in metal to phos- phorusratio.Thecomparisonofvibrationalspectraofvitreousgadoliniummetaphosphate x  0:25 withthoseofits crystallineanalogsrevealsadecreaseinPOPandPO 2 bondanglesinglass.Thechangesobservedareconsistentwithan elongationofP±O  terminalandP±O±PbridgingbondsinthePO 4 tetrahedra.Theredistributionofbandfrequencies is explained with the more covalent interaction of Gd 3 with polyphosphate anions in glasses. The spectra of Gd 2 O 3  0:27 P 2 O 5  0:73 and Gd 2 O 3  0:31 P 2 O 5  0:69 glassescontainthecharacteristicbandsofthemetaphosphatestructure along with features due to vibrations of PO 3 end groups. Their presence is interpreted in terms of the progressive fragmentation of the polyphosphate chains at these glass compositions. Ó 2001 Elsevier Science B.V. All rights re- served. 1. Introduction Metaphosphate glasses containing rare-earth ions have potentially important applications in optical communications and laser technologies [1,2]. Glasses of the RPO 3  3 formula where R represents one of the lanthanide ions) have been reported to exhibit the largest magnetic contribu- tions to the low temperature speci®c heats known in oxide glasses [3]. Sm and Eu phosphate glasses are unusual in having a negative hydrostatic pressure dependence of bulk modulus and a neg- ative coecient of thermal expansion [4]. The promising physical properties of the rare-earth phosphate glasses have initiated many studies of their structure including EXAFS [5], X-ray and neutrondiraction[6,7],Ramanscattering[8]and M ossbauer spectroscopy [9]. Thisworkisapartofourongoingprogramto study the structure of the rare-earth phosphate glasses. Previous investigations on the devitrifca- Journal of Non-Crystalline Solids 293±295 2001) 562±568 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +359-2 979 2552; fax: +359-2 971 2688. E-mail address: dilieva@ipchp.ipc.bas.bg D. Ilieva). 0022-3093/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0022-309301)00778-5