Water-soluble ferroelectric crystals with inhomogeneous impurity distribution

Stabilization of the unipolar state via the formation of inhomogeneous impurity distribution in crystal bulk is considered. Possible growth of crystals with stable characteristics is demonstrated on triglycine sulfate (TGS) crystals with a regular inhomogeneous impurity distribution. The properties of TGS crystals with an inhomogeneous distribution of chromium ions grown above and below the Curie temperature T_C are studied. Inhomogeneous TGS crystals of three types are obtained: type-I crystals with a smooth variation of the concentration gradient along the growth direction, type-II crystals with a periodic layer variation of the impurity concentration, and type-III crystals with a sawtooth-like variation of the impurity concentration along the sample length. The TGS crystals with the regular inhomogeneous impurity distribution in the ferroelectric phase are characterized by higher values of the internal bias field E _b , unipolarity coefficient k, and pyroelectric coefficient γ than the inhomogeneous crystals in the paraelectric phase and the crystals with the statistic impurity distribution grown by the conventional method.     

Formation of an internal bias field in chromium-and L, α-alanine-doped triglycine sulfate crystals

The unipolar state of a chromium-and L, α-alanine-doped ferroelectric triglycine sulfate (TGS) crystal has been studied. The experimental data on the distribution of internal bias fields with respect to a seed are considered. The possible mechanisms of the formation of an internal bias field during the growth of TGS crystals with a low impurity concentration are considered.     

Modification of pyroelectric crystal TGS using thermodynamic theory

Based on the Devonshire thermodynamic theory, the relationship λ/χ = Ps/C can be regarded as a method to increase the pyroelectric material figure of merit of ferroelectric crystals. Several modified TGS crystals doped with urea or co-doped with urea and other dopants have been grown. The effect of the urea dopant on crystal growth and pyroelectric properties was investigated. The pyroelectric figures of merit M (λ/ε) of the doped TGS crystals are obviously higher than those of pure TGS. Furthermore, the variations of λ/χ and Ps/C as a function of temperature for these doped TGS single crystals were measured, and analyzed according to the Devonshire thermodynamic model.     

Nanorelief of the natural cleavage surface of triglycine sulphate crystals with substitutional and interstitial impurities

Ferroelectric triglycine sulphate crystals (TGS) with substitutional (LADTGS+ADP, DTGS) and interstitial (Cr) impurities have been studied by atomic-force microscopy, X-ray diffraction, and X-ray fluorescence. The nanorelief parameters of the mirror cleavage TGS(010) surface have been measured with a high accuracy. A correlation between the crystal defect density in the bulk and the cleavage surface nanorelief is revealed at the submicrometer level.     

New method for the visualization of domain and defect structure of ferroelectrics

A new method for the visualization of domain and real structure of ferroelectric triglycine sulphate (TGS) crystals on the scale of optical microscopy by means of decoration with auramine is developed. Auramine deposits on crystal surfaces as discrete particles about 2 microns in size and as a continuous layer, thus allowing both the domains as a whole and the various electrically active elements of the domain and real TGS structure to be visualized with high resolution. Due to decoration with auramine, the domain structure of TGS detected with a very high contrast; elements of the geometrical relief-cleavage steps exhibiting different electrical properties are also revealed. Furthermore, it has been observed for the first time that the positive domains have sharp electrical boundaries, while the negative domains have erased boundaries. It has also been established that between the domains of opposite signs regions exist characterized by a very low electrical activity. Decoration of annealed TGS crystals which were rapidly cooled from the temperature of 150°C, i.e. above the Curie point (49°C) down to room temperature resulted in detection of new electrically active directions on the surface of the negative domains; these directions are likely to occur in the paraelectric state. The new method cannot only be applied to the study of the TGS crystals but can also be useful in investigation of other ferroelectrics.     

Dielectric properties of triglycine sulfate crystals with defects at low and infralow frequencies

Dielectric responses of several crystals in ultraweak measuring fields at low and infralow frequencies are compared, namely, of nominally pure, Cr-and Lα-alanine-doped triglycine sulfate (TGS) crystals and TGS + Cr³⁺ crystals irradiated with X-rays. It is shown that dopant-induced bias fields give rise to crystal unipolarity, suppress the domain contribution to their dielectric response, and diffuse the phase transition. It is established that X-ray irradiation of the crystals results in “radiation annealing” of TGS + Cr³⁺ crystals, which increases their permittivity and diminishes diffusion of the phase transition.     

Dielectric Spectra of TGS + Сr Crystals in the Vicinity of Phase Transition

Crystallography Reports - Dependencies of the complex permittivity of chromium-doped ferroelectric triglycine sulfate crystals (TGS + Cr) have been measured using dielectric spectroscopy method in...     

Growth kinetics on the (100) and (001) faces of TGS crystals

The growth kinetics and mechanisms on the (001) and (100) faces of TGS crystals were investigated. A phase contrast microscope with a CCD camera was used to observe the growth of the crystal. We found the growth on the (001) and (100) faces at high supersaturation was mainly controlled by a BCF surface diffusion mechanism. The kinetic data for the (100) face were also fitted by the nucleation and layer growth model of two-dimension nucleation at high supersaturation. Some important growth parameters for TGS crystals, such as edge energy, activation energy, and so on, were estimated.     

掺三氟乙酸TGS晶体生长及其性能研究

本文以三氟乙酸作为掺质,分别按4.4mol%、9.4mol%、13.4mol%、18.4mol%的配比进行了掺质TGS晶体生长,并对其作X射线粉末衍射分析及晶体热释电性能的测试。结果表明,三氟乙酸的掺入虽然使热释电性能有一定程度下降,但却使得晶体铁电-顺电相转变延迟,提高了晶体的居里点,并产生了一定的内偏压场。     

Scanning Capacitance Microscopy of Triglycine Sulfate Crystals with the Profile Chromium Distribution

The spatial capacitance distribution, domain wall configuration, and impurity composition of triglycine sulfate TGS–TGS + Cr crystals with a growth periodic impurity structure have been investigated using scanning capacitance microscopy and X-ray fluorescence and topography. The chromium ion concentration in the strips emerging to the surface has been determined, and the periodic impurity distribution has been established. The difference between the chromium concentrations in nominally pure and impurity strips was found to be ~0.08 wt %, which is reflected in a variation in the capacitance image contrast by 0.17%. It is shown that capacitance images carry information about localization of the impurity gradient regions and domain walls and make it possible to establish a correlation between the defect and domain structures of a ferroelectric crystal.     

掺杂TGS晶体的生长及热释电性能研究

选择重稀土离子Dy3 为掺杂阳离子,DL-丙氨酸与L-谷氨酸部分取代甘氨酸分子,生长了不同掺杂配比的TGS晶体。生长和测试实验表明,掺杂TGS晶体较纯TGS晶体易于生长。将掺杂晶体生长溶液的pH值控制在1~4,可改变掺杂晶体的结晶习性。用ICP发射光谱测试了掺杂晶体中稀土元素的含量,用X射线粉末衍射法测定了晶格参数,结果表明:元素已进入晶体,晶格参数稍有变化,但掺杂晶体的对称性仍为C2-2。通过测量掺杂晶体的电滞回线,得到了内偏压场,还测量了各样品的热释电系数、自发极化强度,作了温度曲线,并分析了各掺杂剂对提高热释电性能和锁定极化的作用。结果表明:是有应用前景的热释电材料。     

Growth of TGS crystals using uniaxially solution‐crystallization method of Sankaranarayanan‐Ramasamy

The recently discovered crystal growth method called uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR) is modified in some aspects and used for growth of triglycine sulphate (TGS) crystals. The modification leads to the simplicity, reduction of cost and avoided the temperature fluctuations. The 〈010〉 direction of TGS is very important and used for fabrication of infrared detectors. Using this method, the 〈001〉, 〈010〉 directional crystals of TGS were successfully grown in a glass crystallizer. The grown crystal was characterized by HRXRD, UV‐Visible and dielectric studies. The results prove the suitability of the modified SR method for oriented TGS crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND2CD2COOD)3.D2SO4

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND₂CD₂COOD)₃.D₂SO₄ is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below T_C using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H‐bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long‐range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.     

On growth and morphological studies of TGS single crystals

The effect of various growth parameters; seed morphology, growth-temperature and pH of the mother solution on the growth of TGS single crystals is studied. The effect of these variables on the crystal morphology and perfection is reported. It is shown that; (i) The crystal quality is much dependent on the seed and the growth temperature and (ii) the pH-control is a simple and an effective method for obtaining TGS crystals of required morphology.     

晶体中负离子配位多面体结晶方位、形变与晶体压电、铁电性

本文研究了压电、铁电晶体中负离子配位多面体的结晶方位与形变,提出了压电晶体中同一种负离子配位多面体的结晶方位是一致的.在铁电晶体中,负离子配位多面体发生形变,伴随着晶体发生顺电-铁电相变,并从这一基本过程出发,对铁电体相变的形成机理进行了讨论.     

Vapour diffusion growth and characterisation of fully deuterated triglycine sulphate (ND2CD2COOD)3D2SO4

A new vial-in-vial vapour diffusion method for growing single crystals of fully deuterated triglycine sulphate (TGS) has been developed. Single crystals of hydrogenous TGS were also grown for comparison purposes. The crystals have been characterised using x-ray diffraction and differential scanning calorimetry. The phase transition temperature was 334.0±0.5 K for fully deuterated TGS compared to 322.3±0.3 K for hydrogenous TGS. These values compare well with the expected T_C.     

弛豫铁电单晶的生长及性能优化研究进展

钙钛矿型(ABO₃)弛豫铁电单晶具有优异的机电耦合性能,被认为是研制下一代医疗超声换能器、高精度压电驱动器、水声换能器等机电耦合器件的核心关键材料。针对弛豫铁电单晶材料制备与物理性能方面尚存在的基础科学与工艺问题,本文综述了近些年弛豫铁电单晶生长与性能优化方面的研究进展,包括若干新的单晶生长方法用以改善弛豫铁电单晶的成分和性能均匀性,提升弛豫铁电单晶压电性能的系列新方法,通过铁电畴结构调控以获得高透光率的弛豫铁电单晶,以及高性能弛豫铁电单晶在电光技术领域的应用等。     

Study of the surface heterogeneity of topographic and electric nature by atomic force microscopy by the example of triglycine sulfate

Triglycine sulfate crystals with an ideal (010) cleavage plane are used as model objects to reveal problems in interpreting atomic force microscopy (AFM) images of surfaces with nonuniform charge distribution. Specific microrelief features of two types are found: lenslike formations with different contrast and rounded protrusions/valleys of different size but fixed height. An analysis of their evolution with a change in temperature and under an electric field and mechanical impacts has made it possible to separate relief elements from the crystal domain structure. The interpretation proposed is confirmed by the multimode AFM data. The specific features of the images of dynamic domains and aged domains (which cannot undergo polarization reversal) are studied. The domain-wall width found in the AFM measurements depends on the technique used and the specificity of probe-surface interaction; it varies from 9 to 2000 nm. The most reliable data on the domain-wall width in triglycine sulfate crystals are provided by piezoelectric force microscopy, according to which the wall width does not exceed 30 nm.     

A contribution to the study of the influence of impurities on the growth and some physical properties of TGS single crystals

Single crystals of TGS doped with Ni²⁺, Cu²⁺ and Fe³⁺ have been prepared under identical conditions by the method of temperature decrease (below the phase transition point). Presentation of the influence of impurities on the development of individual crystal faces is based on goniometric measurements. The influence of impurities on the domain structure of TGS is documented by microphotographs of domain structures and by investigation of the variation with time of the average domain width. It is shown that the distribution of impurities (between the liquid and solid phases) is approximately proportional to the concentrations of metal glycino chelates in the solution. From the results concerning the influence of impurities on various physical properties follows that the degree to which the properties are affected depends not only on the impurity concentration but also on the specific intensity of their action which is due to variations in the binding forces in the structure of TGS.     

Investigation for ferroelectric domains by scanning electron microscopy

Examples for the direct observation of domain structures in ferroelectric crystals by means of scanning electron microscopy are given. The results for TGS and AFB crystals with direction of the polarization vector perpendicular to the observed surface are presented with respect to temperature changes, to domain enlargement under the influence of an external electric field and to the influence of X-ray- and γ-radiation on the domain formation.