EFFECT OF HYDROSTATIC-PRESSURE ON THE PHASE-TRANSITIONS IN FERROELECTRIC (CH3NH3)(5)BI2CL11 (MAPCB) AND (CH3NH3)(5)BI2BR11 (MAPBB)

Effect of hydrostatic pressure on the phase transitions and dielectric anomalies has been studied for ferroelectric (CH3NH3)(5)Bi2Cl11(MAPCB) and (CH3NH3)(5)Bi2Br11 (MAPBB)in a pressure range up to about 650 MPa. The Curie temperatures T-c (311 K in h24PCB, 307 K in MAPBB at 0 MPa) increase with increasing pressure with initial pressure coefficients (dT(c)/dp)(p=0) of 0.063K/MPa and 0.060 K/MPa for MAPCB and MAPBB, respectively. In MAPCB, the temperature at which the dielectric constant shows a diffuse anomaly (around 160 K at 0 MPa) increases linearly with increasing pressure with a rate of 0.057 K/MPa. The dielectric anomaly becomes more and more diffusive as pressure increases.