Effect of Hydrostatic Pressure on the Low-Temperature Phase Transitions in Rb2ZnBr4

The effect of hydrostatic pressure on the low-temperature structural phase transitions in Rb_2ZnBr_4 has been investigated by the use of neutron scattering technique. The phase III-to-IV transition temperature, T_3=112 K at atmospheric pressure, increased by applying pressure with a rate of 7 K/kbar. The phase IV-to-V transition temperature, T_4=76 K at atmospheric pressure, decreased by applying pressure with a rate of -45 K/kbar. At high pressure, two high-order pseudo-commensurate phases characterized by wave vectors q_z ≒ (3)/(11) and (4)/(15) were observed in addition to the already known commensurate ones of q_z=(2)/(7) and (1)/(4). The space group of the commensurate phase of q_z=(1)/(4) under high pressure was suggested to be P2_1/c11 from the extinction rule