Dielectric Study of the Phase Transitions in [P(CH_3)_4]_2CuY_4 (Y = Cl, Br)(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Phase transitions in [P(CH_3)_4]_2CuY_4 (Y = Cl, Br) have been studied by dielectric measurements. In [P(CH_3)_4]_2CuCl_4, a slight break and a discontinuous jump on the dielectric constant vs. temperature curve are seen at the normal-incommensurate and the incommensurate-commensurate phase transitions, respectively. A small peak of dielectric constant along the b-direction exists just above the incommensurate-to-commensurate transition temperature. The anisotropic dielectric anomalies of [P(CH_3)_4]_2CuBr_4 at phase transitions were measured along the three crystallographic axes. The pressure-temperature phase diagram of [P(CH_3)_4]_2CuCl_4 was determined. The initial pressure coefficients of the normal-to-incommensurate and the incommensurate-to-commensurate transition temperatures are 0.19 K/MPa and 0.27 K/MPa, respectively. The incommensurate phase in [P(CH_3)_4]_2CuCl_4 disappears at a triple point which exists at 335 MPa and 443 K. The stability and the pressure effects of the incommensurate phases are much different among the four [Z(CH_3)_4]_2CuY_4 crystals (Z = N, P; Y = Cl, Br).
社団法人日本物理学会の論文
2002-05-15