H. E. Müser

Ferroelectric and antiferroelectric properties of deuterated betaine arsenate and betaine phosphate

Abstract The dielectric and thermal behaviour of deuterated betaine phosphate is similar to that of the undeuterated anti-ferroelectric material, but Tc is increased by 69 deg. In deuterated betaine arsenate, however, the low temperature phase is not ferroelectric, as in the undeuterated compound, but anti-ferroelectric.

Critical behaviour in (BPI)x(BP)1−x

Abstract Measurements of dielectric constant, dielectric loss and pyroelectric coefficient as a function of temperature have been performed in Betaine Phosphite (BPI), Betaine Phosphate (BP), and mixed crystals of (BPI)x(BP)1−x for x=0.05; 0.15; 0.30 and 0.60. The behaviour observed for the mixed compounds has a good resemblance to that of structural glasses.

Local polarization in plzt with diffuse phase transition

Abstract In the thermally depoled state, PLZT with diffuse phase transition has no macroscopic polarization in the low temperature region. It is shown, that all anomalies of the properties discussed, can be ascribed to a local polarization.

Ferroelectricity and Antiferroelectricity in Partially Deuterated Betaine Arsenate

Ferroelectric betaine arsenate (BA) becomes antiferroelectric by deuteration. Complete miscibility of BA and deuterated betaine arsenate (DBA) allows the growth of crystals in which the effective interaction, deciding about the transition to a ferroelectric or to an antiferroelectric state, goes to zero. Tc, however, shifts monotonically with the Dcontent, indicating that this interaction is not responsible for the transition itself. Dielectric and caloric data of some crystals with different deuteration degrees are presented.

Dielectric behaviour of betaine arsenate

Abstract The recently discovered ferroelectric material Betaine Arsenate, ((CH3)3NCH2C00)*H3AsO4, shows interesting dielectric properties near the transition temperature Tc ≈ 119 K. Using a model of weakly coupled one-dimensional Ising chains, the temperature dependence both of the dielectric constant and the spontaneous polarization can be well fitted.

Dielectric and pyroelectric behaviour in (BPI)x (BP)1−x

Abstract Measurements of dielectric constant, dielectric loss and pyroelectric coefficient as a function of temperature have been performed in mixed crystals of Betaine Phosphite (BPI) and Betaine Phosphate (BP) ((BPI)x (BP)1−x), for x = 0.80, 0.90, 0.94 and 0.97. The obtained results are compared with the ones previously reported for x = 0.00, 0.05, 0.15, 0.30, 0.60 and 1.00. Three regions are apparent: one where the ferroelectric properties are dominant (x > 0.90), another which can be related to a glassy phase (0.30< x <0.90) and a third one mainly associated with an antiferroelectric behaviour of BP (x < 0.30).

Critical behavior of betaine arsenate

The critical exponents β, γ and δ of undeuterated and partially deuterated ferroelectric betaine arsenate are estimated. Small but remarkable deviations from the tricritical values are observed. The obtained values are tested via scaling of the isothermals.At some distance aboveTc a cross-over of the effective critical exponent γ to a value typically for short-range forces is observed. A suitably defined cross-over temperature range decreases with increasing deuteration and seems to vanish near the antiferroelectric phase boundary.

Temperature Dependence of Spontaneous and Induced Polarization of Betaine Calcium Chloride Dihydrate

Betaine calcium chloride dihydrate (BCCD) is ferroelectric at low temperatures. A sequence of eight transition points separates different commensurate and incommensurate phases with complicated dielectric behavior. On BCCD and the deuterated compound dielectric and caloric measurements are performed to establish the temperature dependence of dielectric constants, coercive fields, critical fields, spontaneous polarizations and induced sublattice polarizations. Additional data about crystal growth and characterization are presented.

Nonlinear behaviour in Betaine Arsenate

Abstract Measurements of complex dielectric constant as a function of a.c. and d.c. electric fields were performed in Betaine Arsenate along the c axis. A strong nonlinear behaviour in the critical region is observed and the two anomalies resolved by the electric field point out the existence of competitive interactions.

Interacting one dimensional Ising spin chains as a model of the layered antiferroelectric squaric acid

Starting from the structure of the layered antiferroelectric squaric acid and assuming an ice rule type interaction mechanism of the protons it is shown that aboveTcthe molecular layers may be considered as a system of parallel and orthogonal nearly independent linear Ising spin chains with strong intrachain and comparatively weak interchain interactions. Whereas the former are treated exactly as nearest neighbour interactions the interchain interactions are taken into account either by the molecular field approximation or, in computer simulations, by nearest neighbour interactions. The parameters of the model are related to the unusually small transition entropy, to the high and nearly temperature independent dielectric constant aboveTc,and to neutron scattering data.