Effect of hydrostatic pressure on the low-temperature phase transitions inRb2ZnBr4

The effect of hydrostatic pressure on the low-temperature structural phase transitions in Rb2ZnBr4 has been investigated by the use of neutron scatter ing technique. The phase III-to-IV transition temperature, T-3 = 112 K at a tmospheric pressure, increased hy applying pressure with a rate of 7 K/kbar . The phase IV-to-V transition temperature, T-4 = 76 K at atmospheric press ure, decreased by applying pressure with a rate of -45 K/kbar. At high pres sure, two high order pseudo-commensurate phases characterized by wave vecto rs q(z) similar or equal to 3/11 and 4/15 were observed in addition to the already known commensurate ones of q(z) = 2/7 and 11/4. The space group of the commensurate phase of q(z) = 1/4 under high pressure was suggested to b e P2(1)/c11 from the extinction rule.