Triglycine Fluoroberyllate Research Articles

Relaxation of static photoelasticity in triglycine fluoroberyllate crystals

The relaxation of the static photoelasticity in triglycine fluoroberyllate crystals has been studied. The anisotropy of the relaxation amplitudes and their anomalies near the phase transition have been revealed. The photoelastic relaxations and peculiarities of their temperature behavior have been explained in terms of the piezocaloric mechanism.

Electron spin echo of Cu2+ in the triglycine sulfate crystal family (TGS, TGSe, TGFB): electron spin–latticerelaxation, Debye temperature and spin–phonon coupling

The electron spin–lattice relaxation ofCu2+ has been studied by the electron spin echo technique in the temperaturerange 4.2–115 K in triglycine sulfate (TGS) family crystals. Assuming thatthe relaxation is due to Raman relaxation processes the Debye temperatureΘD was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe)and 179 K for triglycine fluoroberyllate (TGFB). We also calculated theΘD values from the sound velocities derived from available elastic constants. The elastic Debyetemperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB.The results shown good agreement with specific heat data for TGS. The elasticΘD are considerably larger than those determined from the Raman spin–lattice relaxation. Thepossible reasons for this discrepancy are discussed. We propose to use a modifiedexpression describing two-phonon Raman relaxation with a single variable only(ΘD) after elimination of the sound velocity. Moreover, we show that the relaxation data can befitted using the elastic Debye temperature value as a constant with an additional relaxationprocess contributing at low temperatures. This mechanism can be related to a local mode of theCu2+ defect in the host lattice. Electron paramagnetic resonanceg-factors and hyperfine splitting were analysed in terms of the molecularorbital theory and the d-orbital energies and covalency factors of theCu(gly)2 complexes were found. Using the structural data and calculated orbital energies thespin–phonon coupling matrix element of the second-order Raman process was calculated as553 cm−1 forTGS, 742 cm−1 forTGSe and 569 cm−1 for TGFB.

Simultaneous determination of the birefringence, optical activity and rotation of the indicatrix of triglycine fluoroberyllate

Abstract Triglycine fluoroberyllate (TGFB) undergoes a phase transition at 73°C from a paraelectric high-temperature phase (space group P21/m) to a ferroelecmc phase (space group P21). The optical activity, rotation of the optical indicatrix and birefringence of TGFB along the ferroelectric axis have been simultaneously measured in the paraelectric an ferroelecmc phases using a high-accuracy universal polarimeter (HAUP). The results have been compared with those presented by triglycine sulphate (TGS). The relationships between the spontaneous polarization and the contribution induced by the phase transition in the different optical properties have been analyzed.

Specific heat and thermal conductivity of deuterated triglycine fluoroberyllate

The temperature dependence of the specific heat in deuterated triglycine fluoroberyllate (DTGFB) was measured over the range 294–375 K. The room temperature value was 0.317 cal g −1 K −1 and the jump in C p between the ferroelectric and paraelectric phases is 0.048 cal g −1 K −1. Measurements of the thermal conductivity along the principal crystallographic axes [010], [100], [001] and [110] were temperature independent and had average values of 1.22, 1.61, 1.24 and 1.46 × 10 −3 cal s −1 cm −1 °C −1, respectively. The effects of deuteration on these properties were also examined.

Automated, simultaneous measurement of electrical properties of pyroelectric materials

An automated system for measuring the pyroelectric properties of materials is described. This system can simultaneously measure pyroelectric coefficients and permittivities eliminating errors introduced in the figures of merit by temperature uncertainties. Results on deuterated triglycine fluoroberyllate (DTGFB) are presented.

Single crystal growth and properties of deuterated triglycine fluoroberyllate

A new synthesis technique was used to prepare high purity deuterated triglycine fluoroberyllate (DTGFB). The solubility of DTGFB in D 2O between 20 to 60°C was observed to be significantly different from that of TGFB in H 2O. Significant differences in growth rate and crystal perfection were observed between [010] and [01̄0] seed plates. Specific heat data on DTGFB is reported. The effects of deuteration on lattice parameters and Curie temperature ( T c ) were measured.

Crystal growth from solution using cylindrical seeds

A new cylindrical seed method has been successfully applied to the solution growth of large single crystals of triglycine sulfate (TGS), triglycine fluoroberyllate (TGFB), rubidium acid phthalate (RAP), and L(+) glutamic acid hydrochloride. The method permits the strain free mounting of oriented seed crystals and has resulted in the growth of large crystals of high perfection.

Optical properties of the triglycine sulphate group crystals in the 5 to 22 eV region

Abstract The optical constants of triglycine sulphate (TGS) and triglycine fluoroberyllate (TGFB) crystals have been determined in the 5 to 22 eV region. The changes of the optical constants during the phase transition in TGS have been described, the results obtained agree with certain principles of the vibronic theory of ferroelectricity.

Effect of hydrostatic pressure and deuteration on the order of phase transition in triglycine selenate

It is known that triglycine selenate (TGSe) is isomorphous with triglycine sulphate (TGS) and triglycine fluoroberyllate (TCFB). Each of these crystals shows an order-disorder ferroelectric phase transition of the second order.1-5 This phase transition is accompanied by the change of symmetry 2/m → 2. The behaviour of TGS and TGFB in the vicinity of the phase transition can be well described by a phenomenological theory.2-5 The situation is more complicated in the case of TGSe. The experimental discontinuity of CE at the transition temperature T, exceeds 2.5 times the value predicted by the phenomenological theory.5 Other discrepancies between theoretical and experimental results for TGSe have been found6 Besides that, in TCSe, unlike TGS and TGFB, the maximum permittivity at Tc, (εmax), sharply decreases with increasing hydrostatic pressure p but the difference between the Curie and Curie-Weiss temperatures (Tc - To) increases. A new non-pyroelectric phase with unknown symmetry appears at p > 7 kbar in TGSe.7,8 Recently it was found that the phase transition in deuterated TGSe (DTGSe) was the lst-order one.9 Such unusual behaviour of TGSe requires further examination.

Cluster of four superexchange‐coupled Cu2+ ions in copper‐doped triglycine fluoroberyllate. A theoretical interpretation of the EPR spectrum

AbstractThe unusual EPR spectrum of copper‐doped triglycine fluoroberyllate is shown to originate in large complcx molecules of the hypothetical formula [Cu2+·(NH2CH2COO−)2·H2BeF4]4, built into the distorted host lattice. Superexchange couplings of Cu2+ ions in the cluster through CuFBeFCu paths are discussed. The isotropic superexchange interactions split the 16‐fold degenerate ground crystal state of the four Cu2+ ions into multiplets the further splitting of which, originated by anisotropic interactions, can be described in terms of effective spin Hamiltonians with S = 2 and 1. The observed spectrum is attributed to transitions within the quintet and one of the triplets. By second‐order perturbation procedure, the phenomenological parameters of the effective spin Hamiltonians are expressed in terms of parameters directly describing anisotropic as well as isotropic superexchange interactions in the cluster. The magnitudes of these interactions are thus determined from experimental data.

Thermal expansion of triglycine fluoroberyllate crystals near the ferroelectric transition point

Thermal expansion of triglycine fluoroberyllate crystals near the ferroelectric transition point

EPR Study of Cu2+ Ion in Triglycine Fluoroberyllate

AbstractAn investigation is made of the EPR spectrum of Cu2+ ions in ferroelectric triglycine fluoroberyllate. The values g∥ = 2.24 g∥ = 2.06, and A = 132 cm−1 are similar to those obtained for copper ions in triglycine sulphate and diglycine nitrate. The new lines are typical of S = 1 and the spectrum is found to have an anomaly at the Curie point. The D parameter of the spectrum is linearly dependent on the spontaneous polarization changes.