EFFECT OF MAGNETIC-FIELD AND SI-DOPING ON THE SPIN-PEIERLS PHASE OF CUGEO3

We report the first investigation by elastic neutron scattering under high-magnetic field on CuGe1-xSixO3 with x = 0.3% and 0.7%. For x = 0. 3%, an incommensurate phase is observed above a critical field H-c app roximate to 11.7T, corresponding to a soliton lattice; the superlattic e peak is shifted from its commensurate position along the chain axis by delta k(SP)(c) = 0.007 r.l.u. However, for x = 0.7%, the superlativ e peak remains centered at the dimerization position and shows an incr easing broadening above 6T in all directions.