Dielectric losses in the triglycine sulfate crystal under heating and cooling

Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses ε″ and by the temperature behavior of the maximum losses ε″_max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses ε″_max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat.     

Domain structure of triglycine sulfate family crystals according to the data of piezoresponse force microscopy and their macroscopic dielectric properties

The domain structure of triglycine sulfate (TGS) crystals, specifically nominally pure crystals and those with impurities (LADTGS+ADP, DTSG, and TGS:Cr), is studied by piezoresponse force microscopy (PFM). The measured macroscopic dielectric characteristics are compared with microscopic data on the domain structure of these crystals. The values of the spontaneous polarization, bias voltage, and dielectric permeability as a function of temperature ?(T) are shown to be in agreement with the PFM data. The anomalous behavior of the dependence ?(T) was observed for LADTGS+ADP crystals.     

Investigation of domain structure of TGS single crystal after a transverse electric field by piezoresponse force microscopy

An investigation of the influence of electric field transverse to the ferroelectric axis b_HOP and parallel to c_HOP axis of triglycine sulfate (TGS) single crystal on ferroelectric domain structure was performed by piezoresponse force microscopy. To check if the applied electric field changed the dielectric properties and ferroelectric domain structure the hysteresis loop measurements were carried out as well as observations of domain structure by the liquid crystal technique. The investigation revealed existence of blocked domains in the crystal modified by the electric field TGS.     

Growth,structural, mechanical,spectral and dielectric characterization of NaCl-added Triglycine sulfate single crystals

Pure and sodium chloride (NaCl)-added Triglycine sulfate (TGS) crystals were grown from aqueous solutions by slow evaporation technique. The values of concentration of dopants in the mother solution were 0.2, 0.6 and 1 mol%. The solubility of the grown samples have been found out at various temperatures. The determination of unit cell parameters was carried out by single crystal XRD method and found that the grown crystals crystallize in monoclinic structure. The dielectric characterization for the pure and NaCl-doped TGS crystals was performed by measuring the dielectric parameters like dielectric constant and dielectric loss with various frequencies in the range 10²–10⁶ Hz and with the temperatures ranging from 30 to 70 °C and this study reveals an increase of dielectric constant and loss with the increase of NaCl concentration. Studies on mechanical properties like microhardness and density of the grown pure and NaCl-doped TGS crystals were carried out. UV–Visible transmittance studies were carried out for the grown samples. A sharp fall in the transmittance is observed at 228 nm for pure and NaCl-doped TGS crystals. Atomic absorption spectroscopic (AAS) study was done on the NaCl-doped TGS crystals to ascertain the presence of Na⁺ ions in the lattice.     

Magnetic memory effects in triglycine sulfate ferroelectric crystals

The effect of a magnetic field on the processes of relaxation of the defect structure relaxation in a triglycine sulfate (TGS) ferroelectric (nonmagnetic) crystal has been observed for the first time. The atomic-force microscopy study has shown that the application of a static weak magnetic field (2 T, 20 min) significantly changes the size distribution of defect nanoclusters characteristic of TGS. Previously known macroscopic aftereffects of the magnetic field in TGS (slow relaxation of the dielectric susceptibility, symmetrization of P–E dielectric hysteresis loops, etc.) can be explained by the redistribution of pinning centers of domain walls caused by the magnetically induced reconfiguration of the defect structure.     

(111)取向(Pb,La)TiO3铁电薄膜中90°纳米带状畴与热释电性能的研究

采用射频磁控溅射技术在Pt/Ti/SiO₂/Si(100)衬底上生长了掺镧钛酸铅(PLT)铁电薄膜.用X射线衍射技术(XRD)研究了PLT薄膜结晶性能，结果表明PLT薄膜为 (111)择优取向钙钛矿相织构.使用原子力显微镜(AFM)和压电响应力显微镜(PFM) 分别观察了PLT薄膜的表面形貌和对应区域的电畴结构.PFM观察显示PLT薄膜中存在90°纳米带状畴，电畴的极化为首尾相接的低能量的排列方式，带状畴的宽度为20—60nm.研究了PLT10铁电薄膜的制备条件与性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数ε_r为365、介电损耗tgδ为0.02，热释电系数γ为2.18×10^-8C·(cm²·K)^-1，可以满足制备非制冷红外探测器的需要. 关键词： PLT薄膜 电畴 PFM 极化     

Permanent polarization in pyroelectric TGS in detectors due to x-rays

The dielectric constant, pyroelectric coefficient, and loss tangent of triglycine sulphate (TGS) crystals that had been poled and subsequently irradiated with x-rays are presented as a function of x-ray exposure and temperature. The results are compared with similar measurements made on poled Co⁶⁰ gamma irradiated TGS. An estimated x-ray dosage of 1.5−2.0 × 10⁶ R min^-1 for 1–2 min gave equivalent results to 2.3 Mr of Co⁶⁰ gamma rays in achieving optimum non-ferroelectric pyroelectric in TGS ir detectors.     

Surface morphology, chemical contrast, and ferroelectric domains in TGS bulk single crystals differentiated with UHV non-contact force microscopy

Ferroelectric bulk single crystals of tri-glycine sulphate (TGS) have been investigated in ultra-high vacuum (UHV) using dynamic force microscopy (DFM) in the non-contact (nc) mode. Both chemical contrast from different sub-unit cell cleavage steps, and ferroelectric domains were differentiated by recording the variation in interaction force affecting the excitation amplitude A_exc applied to the piezo shaker in constant amplitude DFM. No chemical difference was found for steps measuring half the unit cell height b, in contrast to b/4—steps where sulphate ions change the local short-range chemical forces. By varying the bias voltage applied to the TGS counter electrode, the sign of bound surface charge within each ferroelectric domain was determined. Domain walls separating regions with antiparallel polarisation vectors are resolved down to a 9 nm domain wall width. Furthermore, we achieved atomic resolution with nc-DFM on cleaved TGS samples indicating the monoclinic unit cell at the ferroelectric sample surface with a=1.0±0.05 nm, c=0.55±0.05 nm, and β=107±3°.     

Growth of 4-(dimethylamino) benzaldehyde doped triglycine sulphate single crystals and its characterization

Single crystals of triglycine sulphate (TGS) doped with 1 mol% of 4-(dimethylamino) benzaldehyde (DB) have been grown from aqueous solution at ambient temperature by slow evaporation technique. The effect of dopant on the crystal growth and dielectric, pyroelectric and mechanical properties of TGS crystal have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters. FTIR spectra were employed to confirm the presence of 4-(dimethylamino) benzaldehyde in TGS crystal, qualitatively. The dielectric permittivity has been studied as a function of temperature by cooling the sample at a rate of 1 °C/min. An increase in the Curie temperature T_c=51 °C (for pure TGS, T_c=48.5 °C) and decrease in maximum permittivity has been observed for doped TGS when compared to pure TGS crystal. Pyroelectric studies on doped TGS were carried out to determine pyroelectric coefficient. The Vickers's hardness of the doped TGS crystals along (0 1 0) face is higher than that of pure TGS crystal for the same face. Domain patterns on b-cut plates were observed using scanning electron microscope. The low dielectric constant, higher pyroelectric coefficient and higher value of hardness suggest that doped TGS crystals could be a potential material for IR detectors.     

Dielectric responses of composite films based on P(VDF-TrFE) copolymer with TGS inclusions

The dielectric characteristics of film samples of P(VDF-TrFE) + TGS composite in the frequency range of 10³–10⁷ Hz are studied. The values of the real and imaginary parts of the complex dielectric constant in the temperature range of–40 to 140°C, including the points of the polymer matrix’s transition to the glassy state when T_g ≈–25°C and the ferroelectric phase transition. An analysis of the ferroelectric crystal inclusion effect on the dielectric response of P(VDF-TrFE) copolymer matrix is carried out.     

The impedance-characteristic method in the study of specific temperature features of dielectric anomaly suppression in triglycine sulfate

The reflection and absorption coefficients in a waveguide loaded on ferroelectric triglycine sulfate (TGS), which has a layered domain structure near the phase transition, are calculated by the impedance-characteristic method. The calculated and experimental data do not reveal any correlations with the specific temperature features in the TGS dielectric response to microwave irradiation. The mechanism of the microwave effect is discussed.     

Ferroelastoelectric phenomena in a uniaxial ferroelectric TGS crystal

Possibility of the ferroelastoelectric behavior manifestations in a uniaxial ferroelectric TGS crystal was investigated. Analysis of the spontaneous piezoelectric moduli tensors for each of the 180°-domains formed as a result of the phase transition in TGS revealed possible directions for simultaneous application of the electric field and mechanical stresses to induce the switching effect in TGS. Influence of the uniaxial mechanical stresses σ₁₁, σ₂₂, σ₃₃ on the parameters of saturated and unsaturated dielectric hysteresis loops in TGS is considered. It was found that a nontraditional E ₃σ₁₂ combination of fields may lead to the domain switching in TGS crystals.     

Single crystals of triglycine sulphate containing palladium

Single crystals of TGS doped with Pd₂₊ have been grown from aqueous solutions using the method of temperature decrease. It was found that the relative growth rate along thec-axis is not constant through the growth process being larger by more than an order of magnitude (in medium size crystals, ca. 30 g) than in pure TGS crystals. Investigation of the domain structure revealed that in the growth pyramids ¦110¦, the crystals are poled in one direction. The internal bias field in these growth pyramids was experimentally found to be of the order of 1 kV/cm. The high internal field excludes the possibility of spontaneous depoling and makes the Pd²⁺-doped TGS crystals suitable for pyroelectric applications.     

Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1-20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30-60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature (T_C) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P-E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (ΔE) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.     

Single crystal neutron diffraction study of triglycine sulphate revisited

In order to get the exact hydrogen-bonding scheme in triglycine sulphate (TGS), which is an important hydrogen bonded ferroelectric, a single crystal neutron diffraction study was undertaken. The structure was refined to an R-factor of R[F ²] = 0.034. Earlier neutron structure of TGS was reported with a very limited data set and large standard deviations. The differences between the present and the earlier reported neutron structure of TGS are discussed.      

SrHf0.67Ti0.33O3 high-k films deposited on Si by pulsed laser deposition

Abstract: The large band gap (3.58?eV) and dielectric properties (?? _r =50) of bulk SrHf_0.67Ti_0.33O₃ (SHTO) make it a promising high-k material. SHTO films were deposited on p-type (100) Si single crystal substrates by pulsed laser deposition. The composition, structure, thickness, and roughness of the SHTO films have been studied using X-ray Photoelectron Spectroscopy, X-ray reflectivity, transmission electron microscopy, and atomic force microscopy. The capacitance?Cvoltage and leakage current density characteristics of the films have been evaluated. For a post-annealed SHTO film with a thickness of 25 nm, the relatively high permittivity of 35 was achieved with the low leakage current density of 4.96×10^?4?A/cm² at ?2?V bias voltage.     

Dielectric properties of film materials based on polyethylene terephthalate and polycarbonate with ferroelectric inclusions

The dielectric properties of film materials based on polyethylene terephthalate and polycarbonate with inclusions of triglycine sulfate (TGS) and TGS with admixture of L, ??-alanine (ATGS) have been studied. An increase in the temperature of the phase transition in these materials as compared to in bulk TGS and ATGS has been revealed.     

Effects of composition ratio on structure and phase transition of ferroelectric nanocomposites from silicon dioxide nanoparticles and triglycine sulfate

The present work is devoted to study on influences of silicon dioxide nanoparticles (SiO₂) on structure and phase transition of a classical ferroelectric of triglycine sulfate (TGS) by synthesizing a composite containing SiO₂ and TGS at different composition weight ratios. Particle size analysis, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) techniques were utilized to charaterize the synthesized composite. The experiments for investigation of phase transition were conducted from 20 to 120°C under a weak electric field (1?V.cm^?1) at 1?kHz. The results revealed an expansion of ferroelectric phase of TGS by 15–55°C with increasing the SiO₂ content. Besides, an additional phase transition point which is characteristic for the bulk clusters of TGS was found at low content of SiO₂. The detected anomalies were discussed thoroughly based on the interaction between components in the composite.     

Raman spectroscopic investigations of epitaxial BiFeO3 thin films on rare earth scandate substrates

BiFeO₃ epitaxial thin films fabricated by pulsed laser deposition on different scandate substrates were investigated by means of Raman spectroscopy. We observed periodic changes in Raman position, full width at half maximum and intensity for some phonon modes as a function of the azimuthal angle ϕ. Further analysis revealed the possibility to assign the so far controversial discussed Raman modes at low wavenumbers (<250 cm⁻¹) through rotational Raman measurements at different azimuthal angles, which show high sensitivity to the aforementioned parameters. Furthermore, the ferroelectric/ferroelastic domain structure shown by piezo‐response force microscopy investigations of the samples was confirmed. Our results are supported by symmetry‐based calculations including the analysis of Raman scattering geometry as well as the dielectric function of BiFeO₃ in the infrared range. Copyright © 2015 John Wiley & Sons, Ltd.     

Dependence of the coercive force on the magnetic field sweep rate in (PrDy)(FeCo)B alloys

The dependence between the coercive force and the average hysteresis loop record time was revealed in sintered (Pr_{1 – x} Dy _x )₁₃(Fe_{1 – y} Co _y )₇₉B₈ magnets. The coercive force was established to grow by 22% with an increase in the average hysteresis loop sweep rate within a range of 1.1 × 10²–3 × 10⁵ Oe/min, obeying a logarithmic dependence on the loop passage velocity with saturation at low rates. Some domain structure transformations produced by a magnetic field in the process of magnetization were established by magnetic force microscopy.