C. Klimm

Glass behaviour in the solid solution of deuterated betaine phosphate0:15 betaine phosphite0:85

For a deuterated solid solution of 15% antiferroelectric betaine phosphate (BP) and 85% ferroelectric betaine phosphite (BPI), measurements of the dielectric permittivity at frequencies 20 Hz< <1 MHz are reported. The freezing phenomena in DBP0.15 DBPI0.85 reveal the characteristics of a transition into a dipolar glass state with peculiarities due to the quasi-one-dimensional structure. Using the Kutnjak model a glass temperature of 25 K is estimated for deuterated DBP0.15 DBPI0.85 and one of 10 K for protonated BP0.15 DBPI0.85 . The relaxation time distribution extracted from the experimental data by means of Tikhonov regularization and calculated in the region of the dielectric dispersion shows an asymmetric behaviour especially at lower temperatures, which is interpreted as being caused by a Gaussian distribution of activation energy and double-well potential asymmetry as well.

Structural phase transitions in partially deuterated betaine phosphite crystals studied by dielectric and electron paramagnetic resonance methods

Abstract Partially deuterated betaine phosphite (DBPI) crystals were investigated by measurements of the dielectric constant and by means of electron paramagnetic resonance (EPR). Two phase transitions could be detected in the temperature range from 100 K to 380 K: a high-temperature phase transition at Tc1 = (355 ± 3) K and a ferroelectric phase transition at Tc2 = (297 ± 3) K. The EPR studies show that the ferroelectric phase transition is related to the simultaneous ordering of the protons and deuterons in the O-H/D… O bonds.

Dielectric properties in the vicinity of the ferroelectric phase transition in a mixed crystal of deuterated BP0.01BPI0.99

The dielectric behaviour of ferroelectric hydrogen bonded deuterated betaine phosphate0.01 betaine phosphite0.99 is investigated in the region of the ferroelectric phase transition. Dielectric dispersion is investigated in the frequency range up to 12 GHz. The dielectric dynamics of a small admixture such as 1% BP is already able to change noticeably the character of the phase transition as well as the quasi-one-dimensional feature of deuterated betaine phosphite. The Debye type dispersion shows a critical slowing down. The frequency of the relaxational soft mode in the paraelectric phase varies according to the quasi-one-dimensional Ising model and decreases down to 0.55 GHz at the phase transition temperature (TC = 299 K). The activation energy for the deuteron flipping motion amounts to ΔU = 3.6kTC = 0.095 eV. The obtained results show the order-disorder character of the proper ferroelectric phase transition. However, the small admixture of 1% betaine phosphate changes noticeably the character of the phase transition as well as the quasi-one-dimensional feature in comparison to pure deuterated betaine phosphite.

Coexistence of glass and ferroelectric order in deuterated betaine phosphate0.05 betaine phosphite0.95 crystals

The dielectric spectra of ferroelectric hydrogen bonded betaine phosphate0.05 betaine phosphite0.95 (DBP0.05DBPI0.95) was investigated in the very wide temperature (300–20 K) and frequency (20–35 GHz) regions. The dielectric dispersion was analyzed in terms of distribution of relaxation times, using Tichonov regularization method. Strongly asymmetric and broad distribution of relaxation times below ferroelectric phase transition temperature T c ≈ 253 K clearly differs from the one that is usually observed in ferroelectrics. The observed disorder in deuterons system close to ferroelectric phase transition temperature is an embryo of coexistence ferroelectric order and dipolar glass disorder observed at low temperatures.

Proton glass behaviour in a solid solution of -irradiated betaine phosphate0.15 betaine phosphite0.85

Measurements of the dielectric permittivity are reported for a solid solution of antiferroelectric betaine phosphate and ferroelectric betaine phosphite at frequencies . The freezing phenomena in reveal the characteristics of a transition into a dipolar glass state. The activation energy was found to be K and an external bias field lowers this value to 513 K.

Spontaneous polarisation in the mixed ferroelectric DBP x DBPI1-x crystals

Abstract Thermal behaviour of spontaneous polarisation, obtained from pyroelectric measurements of ferroelectric hydrogen bonded deuterated (betaine phosphate) x (betaine phosphite)1-x is investigated for x = 0.01 0.03 and 0.05. In the region of the ferroelectric phase transition the spontaneous polarisation is explained by quasi-one-dimensional Ising model. Spontaneous polarisation saturates at 1.8 and 0.16μC/cm2 for DBP0.01DBPI0.99 and DBP0.03DBPI0.97, respectively.

Broadband dielectric spectroscopy of betaine phosphate0.03 betaine phosphite0.97 crystals in the vicinity of the ferroelectric phase transitions

The dielectric properties of ferroelectric hydrogen bonded betaine phosphate0.03 betaine phosphite0.97 (BP0.03BPI0.97) have been investigated in the region of the ferroelectric phase transition. Dielectric dispersion was investigated in the frequency range up to 53 GHz. The distribution of relaxation times has been calculated directly from the dielectric spectra. The parameters of the double-well potentials of the hydrogen bonds, the local polarization distribution function and the average (macroscopic) polarization have been extracted from the dielectric measurements data. At low temperatures the freezing phenomena in BP0.03BPI0.97 revealed the complex dielectric permittivity behavior characteristic for transition into the dipolar glass state. The activation energy of this low temperature process was equal to E b  = 558 K (0.048 eV) and the freezing temperature was estimated on 30 K.

Proton glass behaviour in a solid solution of -irradiated deuterated

Measurements of the dielectric permittivity are reported for a deuterated solid solution of -irradiated antiferroelectric ferroelectric at frequencies . The freezing phenomena in revealed the characteristics of a transition into a dipolar glass state. The activation energy was found to be (0.027 eV). The Kutnjak model showed a non-typical glass behaviour with an estimated glass temperature of 55.4 K.

Dielectric investigation of a solid solution of deuterated betaine

Measurements of the dielectric permittivity are reported for a solid solution of deuterated antiferroelectric betaine and ferroelectric betaine at frequencies in the range . This crystal orders antiferroelectrically at . The dielectric response over the whole of the temperature region 50 - 300 K shows ac and dc conduction. The activation energy of the dc conduction was found to be (0.015 eV).

Radio and Microwave Spectroscopy of the Betaine Phosphate/Betaine Phosphite Mixed Crystals

The dielectric behaviour of ferroelectric hydrogen bonded deuterated betaine phosphate x /betaine phosphite 1 m x (DBP x DBPI 1 m x ) crystals with x = 0.01, 0.03 is investigated in the region of the ferroelectric phase transition. A small admixture of betaine phosphate is already able to change noticeably the character of the phase transition of deuterated betaine phosphite. In ferroelectric phase the distribution function of the relaxation times of DBP 0.03 DBPI 0.97 broaden continuously with the temperature decrease and deviate from the monodispersive character. The real distribution of the relaxation time of both mixed crystals have been obtained. The temperature behaviour of the local polarization distribution function confirms the inhomogeneous ferroelectric properties of the deuterated betaine phosphite with 3% admixture of betaine phosphate.