TGSe Crystals Research Articles

Temperature Dependence of Ferroelectric Mode Frequency, Dielectric Constant and Loss Tangent in Deuterated TGSe Crystal

By fitting model values of physical quantities for deuterated TGSe crystal in theoretically derived expressions for ferroelectric mode frequency, dielectric constant and loss tangent in our earlier paper temperature dependences of these quantities have been calculated. Present results agree with experimental data of literature value.

Electronic band structure and optical properties of ferroelectric TGS, TGSe and TGFB crystals

Structural and electronic properties of the ferroelectric TGS, TGSe and TGFB crystals were studied by the ab initio method in the framework of the density functional theory. Equation of state (total energy vs. unit cell volume), band structure, density of electronic states and dielectric functions in the range of valence electrons excitations have been calculated using the plane waves and pseudopotentials. The comparable structural and electronic characteristics of TGS, TGSe and TGFB crystals are obtained for the first time and discussed in relation to the reference experimental data. The semiempirical dispersion-correction approach implemented in CASTEP code has been applied to the materials studied and has been shown to produce results more close to the experimental data. Correlation of the total energy difference Ep – Ef for paraelectric and ferroelectric phases and Curie temperatures of the ferroelectric phase transitions has been revealed for TGS, TGSe and TGFB crystals, that was not reported before.

Study on Pyroelectric Properties of the TGS-TGSe Crystals with Internal Electric Field

Measurements of spontaneous polarization and pyroelectric coefficient versus temperature and electric field were performed for the TGS–TGSe crystals at a definite internal electric field. The obtained results are compared with the thermodynamic theory predictions. The temperature and electric field dependencies of pyroelectric coefficient are presented together with its maximal value as a function of the electric field intensity. It was shown that the temperature, at which the pyroelectric coefficient reaches its maximal value, depends on the external electric field.

Splitting of the phase transition in TGSe crystal under uniaxial stress

Changes in the velocity and attenuation coefficient of quasi-longitudinal waves propagating in TGSe crystal in the direction X induced by uniaxial stress σY were measured in the temperature range of ferroelectric phase transition. The application of uniaxial stress was found to shift the phase transition temperature by ∂TC/∂σY = −0.18 K/MPa. For the stress greater than 2 MPa an additional anomaly in the wave velocity and attenuation appears, which has been interpreted as a splitting of the phase transition.

Influence of uniaxial stress on ultrasonic wave propagation near thephase transition in a TGSe crystal

Changes in the velocity and attenuation coefficient of quasilongitudinal wavespropagating in a TGSe crystal in the directions z' = z-4°and x, induced by uniaxial stress σx and σy, were measured in the temperature range of the ferroelectric phasetransition. The uniaxial stress applied was found to shift the phasetransition temperature by ∂TC/∂σx = -0.074 and∂TC/∂σy = -0.18 K MPa-1. Othereffects appearing under the influence of external stress, such as a change inthe jump of the wave velocity at the phase transition, increase in theattenuation coefficient and broadening of the phase transition range, arediscussed on the basis of the phenomenological theory. The relaxation time ofthe order parameter fluctuations was determined. For stress exceeding 2 MPa anadditional anomaly in the wave velocity and attenuation appeared, which wasinterpreted as a splitting of the phase transition. The nonlinear elasticeffects at the phase transition, in the para- and ferroelectric phases, arealso discussed.

Defects and phase transformation in TGSe and DTGSe crystals

The specific heats of TGSe and DTGSe crystals, pure and γ-irradiated, were measured. The influence of radiation defects on the phase transition in ferroelectric crystals was studied by calorimetric experiments. The Landau free energy expansion coefficients were measured for various doses of γ-irradiation (0 < D < 5 MR). The order of the phase transition changed from the first to the second through the tricritical point in DTGSe crystal.

Linear birefringence derivatives for TGSe and TGFB ferroelectric crystals

Temperature dependence of the linear birefringence (1.b.) in TGSe and TGFB crystals has been studied with a high temperature resolution. Temperature derivatives of the 1.b. are compared with the specific heat transients measured for these crystals.

Temperature dependence of the order parameter at the quasi-tricritical phase transition in ferroelectric TGSe

The order parameter temperature dependence near Tc has been studied in TGSe crystals with two different experimental techniques: spontaneous polarization (hysteresis loops) and increment of birefringence by means of high resolution measurements. The values of g and h, characteristic dimensionless parameters in the equation of state, are obtained, confirming the previous result g ≈ 1/3, which corresponds to quasi-tricritical behavior.

The effect of uniaxial pressure on the ferroelectric phase transition of TGSe crystals

Isobaric studies of the influence of uniaxial pressure on the transitions of pure TGSe crystals for the three directions are reported. The critical exponents, and , from dielectric constant and hysteresis loop measurements, as well as the coefficients and of the fourth and sixth powers of P in the free-energy expansion under uniaxial pressure were determined. It has been found that uniaxial pressure applied along the -axis keeps the transition near a tricritical point for 0 < X < 200 bar, but that when it is applied along the b- and c-axes it strengthens the second-order phase transition behaviour. The tricritical behaviour of TGSe crystals is discussed and a possible driving mechanism for the change in order of the phase transition is proposed.

Dielectric losses behaviour under frequency and a.c. field amplitude variation in TGSe crystals

Dielectric losses in triglycine selenate crystals were studied in the frequency range from 20 Hz to 1 MHz for several a.c. field amplitudes. The peculiar shape of the temperature dependence of the loss factor D = tan δ reflects the character of the phase transition, which is very close to tricritical. In the range from 20 Hz to 10 kHz the temperature behaviour of tanδ is described according to the model presented previously for TGS crystals, adapted to the TGSe, taking into account the specific features of the phase transition. A low and a higher frequency relaxation band in D vs. frequency were found and a dip in D was noticed in the range of a few kHz for several temperatures near and below T C. The relaxation frequency attributed to domain wall motion increased rapidly, reached a maximum around 3 K below T C' and then dropped in relative value toward lower temperatures, as it has been observed in other ferroelectric transitions.

Evidence of tricritical behavior in DTGSe crystal under γ-irradiation

Abstract The specific heat of a partly deuterated TGSe crystal–pure and γ-irradiated—has been measured. It is shown that small doses of radiation (DC 0.5 MR) produce a change of the phase transition order through the tricritical point. The dose dependence of the Landau coefficients for DTGSe (x = 0.62) was found.

Defects and ferroelectric phase transitions

Abstract With TGSe crystal as an example the y-irradiation effects upon the ferroelectric phase transition including dose dependence of Landau expansion coefficients are considered and the interpretation of the results is given.

Effect of √-irradiation on the structure and dynamics of domains in triglycine selenate

Abstract A comparative study of the switching properties of pure and √-irradiated TGSe crystals has been carried out to see the effect of irradiation on the structure and dynamics of domains. The switching behaviour of √-irradiated TGSe has been found to be qualitatively similar to that of unirradiated crystal and this has been interpreted in terms of structural inhibition caused by the formation of radiolysis products as well as the difference between the domain structures of the unirradiated and irradiated samples. Confirmation of this has been obtained by studying the domain patterns using the etch method.

Study of pyroelectric properties of TGSe and DTGSe crystals

Abstract The problem of crystal craking has been solved by using of synthetic method with modified raw materials. Large TGSe and DTGSe single crystals with high qualities have been grown. Such parameters as pyroelectric coefficient, relative dielectric constant and loss tgδ have been measured. Meantimes, this paper also analyses the advantages and disadvantages as well as the prospect of these two crystals in their applications as pyroelectric materials.

Optical activity of TGSe crystals

Abstract Dispersion of optical rotatory power σ temperature dependence of σ and electrogyration hysteresis loop of TGSe crystals have been measured. The origin of OA in TGS type crystals is discussed.

Domain-wall orientations and domain shapes of ferroelectric TGS and TGSe crystals

Wall-energy density as a function of wall orientation has been calculated on the basis of Zhirnov-type domain-wall theory. The equilibrium wall-orientations and the domain shapes which are consistent with the experimental observations have been successfully brought about for TGS and TGSe crystals. Two preferential orientations in TGSe are mainly due to the tri-critical nature of the ferroelectric phase transition.

E. P. R Study Of Copper (II) - Doped Triglycine Selenate (TGSe)

Abstract The angular dependence of EPR of the Cu2+ ion in the ferroelectric TGSe crystal has been investigated. The coordination of the Cu2+ ion and the number of complexes were found to be the same as in the isomorphous copperdoped TGS crystal. The spin density on the central metal ion indicates a more covalent nature of the Cu-ligand bond in TGSe. The spectroscopic splitting factor exhibits an anomaly near the ferroelectric transition point.

Dielectric, piezoelectric, elastic properties and internal friction of TGSe crystals with large unipolarity

AbstractIn this work we have studied influence of temperature and external electric field on dielectric, elastic, piezoelectric properties and internal friction of D, L‐α‐alanine doped triglycine selenate crystals. Experimental result analysis allows to conclude that ferroelectric materials with stable physical properties may be created on doping crystals foundation.

Depolarization field effect on the brillouin scattering spectra in TGS and TGSe

Abstract Brillouin scattering spectra have been observed in TGS and TGSe crystals. The directions of the observed longitudinal or quasi-longitudinal phonon vector q were: (1) q // c axis, (2) q // b axis, and (3) q deviates 5 degrees from the c axis in the (100) plane. The anisotropic behavior of the spectra is interpreted by taking account of the depolarization field.

Critical behaviour and internal bias of TGS and isomorphous crystals depending on growth conditions

AbstractThe critical behaviour of TGS and isomorphous DTGS, TGSe and DTGSe single crystals grown at various conditions was investigated. The growth dependences for ΔT in heating and cooling regimes and shift ΔT of the temperature of maximal permittivity were found. These dependencies were explained in terms of existence of internal biasing fields these being measured vs temperature.