HYDROSTATIC-PRESSURE EFFECT ON COMMENSURATE INCOMMENSURATE TRANSITION IN K2SEO4-ELASTIC ANOMALIES STUDIED BY BRILLOUIN-SCATTERING

A Brillouin scattering study of the commensurate-incommensurate transition in K//2SeO//4 submitted to a hydrostatic pressure was performed. It was found that an increasing pressure lowers te transition temperature (dT//i/dP//i equals minus 59 K/GPa). The strong anomalies of velocity and damping of the longitudinal acoustic wave propagating along left bracket 001 right bracket are weakly affected when pressure acts. The effect of pressure on these anomalies has been calculated on the basis of the lowest order couplings eQ**2 and e**2Q**2 between strain e and order parameter Q.