Effect of the uniaxial stress on the dielectric properties of antiferroelectric cupric formate tetrahydrate

摘要

The real and imaginary parts of complex relative permittivity along the b axis of antiferroelectric Cu(HCOO)24H2O single crystals were measured at 1 kHz over a temperature range -10 to -45 °C under various uniaxial stresses. The antiferroelectric phase transition temperatures (ϑc) under uniaxial stress along the c axis (σ3) and the a′ axis (σ1) vary linearly with the stress coefficients of dϑc/dσ3=3.3×10-8 K/(N/m2) and dϑc/dσ1=2.6×10-8 K/(N/m2), respectively, and these values agree well with the values calculated by the Clausius‐Clapeyron equation. The temperature dependence of the real part of complex permittivity in the paraelectric phase under various uniaxial stresses obeys the Curie‐Weiss law. The characteristic temperatures (ϑ0) under σ3 and σ1 vary linearly with the stress coefficients of dϑ0/dσ3=-6.7×10-7 K/(N/m2) and dϑ0/dσ1=-10.8×10-7 K/(N/m2), respectively. The dielectric properties under uniaxial stresses are elucidated by the phenomenological theory for the antiferroelectrics under uniaxial stresses, and the electrostrictive coefficients are estimated from the stress dependence of ϑc and ϑ0. The activation energy for the flip‐flop of the dipole (Δϕ) is found to increase with applied stresses, and γ which stands for the stress dependence of Δϕ has a large anisotropy and its values are 1.1×10-9/(N/m2) along the c axis and 60.0×10-9/(N/m2) along the a′ axis.