A high-pressure vibrational study of metal pyrophosphate materials /

The effect of high external pressures on the Raman spectra of various metal pyrophosphate salts has been investigated with the aid of a diamond-anvil cell and a Raman microspectrometer. The pressure dependences of the Raman-active bands were determined from the wavenumber vs. pressure plots. The KMHP2O7·2H2O [M = Co(II), Mn(II), Zn(II) and Mg(II)] series of salts was studied at pressures up to about 50 kbar (ca. 50,000 atm). The Co(II) salt displayed an irreversible, pressure-driven, structural transformation at around 29 kbar. The M4(P2O 7)2·10H2O [M = Zn(II) and Mn(II)] salts were also investigated. A reversible phase transition was observed to take place for the Zn(II) salt in the pressure range of 15-20 kbar. Three other pyrophosphate materials, K4P2O7, Co 2P2O7·6H2O and Ca2KH 3(P2O7)2·3H2O, were also examined at high-pressure, but no pressure-driven phase transitions were observed in these cases