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Raman studies of some alkali metal–lanthanide double tungstates at high pressures
Author(s) -
Jayaraman A.,
Sharma S. K.,
Wang S. Y.
Publication year - 1998
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199804)29:4<305::aid-jrs241>3.0.co;2-p
Subject(s) - scheelite , wolframite , monoclinic crystal system , raman spectroscopy , lanthanide , alkali metal , chemistry , phase transition , crystallography , phase (matter) , tungsten , crystal structure , ion , thermodynamics , physics , organic chemistry , optics
Pressure‐induced phase transitions in five alkali metal–lanthanide double tungstates, ALn(WO 4 ) 2 , were investigated using high‐pressure Raman spectroscopy in the range 0–35 GPa. A phase transition in the scheelite‐type double tungstates NaSm(WO 4 ) 2 , NaTb(WO 4 ) 2 and NaHo(WO 4 ) 2 to a distorted monoclinic type occurs near 10 GPa. In the pseudo‐scheelite‐type KLa(WO 4 ) 2 a similar pressure‐induced transition occurs. The behavior is compared with the scheelite‐type SrWO 4 and it is proposed that the local compressibility difference at the cationic sites drives the transition in the Na and K double tungstates. The results suggest that the scheelite‐type lattice becomes unstable near 10 GPa. In LiY(WO 4 ) 2 , which has the β‐LiYb(WO 4 ) 2 ‐type structure (wolframite‐like), a sluggish phase transition to a different monoclinic lattice occurs, which upon release of pressure reverts to the wolframite‐type structure. A brief account of the crystal chemistry of the alkali metal–lanthanide double tungstates from the extensive Russian literature is presented to obtain an insight into the pressure‐induced phase transitions in them. © 1998 John Wiley & Sons, Ltd.