Structure of the polar (010) cleavage of a ferroelectric TGS crystal from the atomic-force microscopy data

The atomically smooth polar (010) cleavage of a ferroelectric triglycine sulfate (TGS) crystal has been studied by the method of atomic-force microscopy. It is shown that the rounded 0.6-nm-high (deep) protrusions and pits with nanometer lateral dimensions revealed on the surfaces of TGS crystals are characteristic of their microrelief. These microrelief details can be formed either as a result of crystal cleavage in the ferroelectric phase or the mechanical action of a cantilever onto the crystal surface. These two-dimensional formations are relatively stable and genetically related to the layer structure of the ferroelectric phase of TGS crystals.     

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.     

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.     

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.     

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.     

Application of different atomic force microscopy methods for detailed diagnostics of gold nanocoatings on a single-crystal sapphire surface

Gold nanodots and clusters deposited on sapphire substrates with a regular nanorelief have been investigated by atomic force microscopy. It is shown that the phase-contrast method combined with contact force spectroscopy makes it possible to identify these nanostructures and describe some of their physical properties.     

Investigation of the Solution Status of TGS and ATGSP Crystals

This paper reports on the solubility curves of TGS and ATGSP crystals with different pH's. The relationship of (010) growth rate in solutions with different pH varied with the supersaturation, has been studied. The influence of pH on the metastable region of solution have been measured. The experimential results are discussed with respect to the structure and viscosity of solution and the solubility of the crystals. Finally the optimum conditions for the rapid growth of TGS and ATGSP crystals is given.     

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.     

Study on the Growth of Triglycinsulphate Single Crystals

Crystallization of TGS at 52.0°C - above the transition point - has been studied in a wide range of supersaturation of the solution (σ = 0 to 10⁻²). The rates of growth of {110} and {001} faces were measured as a function of supersaturation at constant hydrodynamical conditions (Re = 3.4 · 10⁻³). Further, the influence of hydrodynamical conditions on the growth of {110} faces at constant supersaturation (σ = 4.2 · 10⁻³) was established. The parameters of the experimentally found dependences are determined on the basis of the surface-diffusion model of BURTON . CABRERA and FRANK . From these dependences follows that the growth rate of the {110} faces is already almost limited by the volume diffusion of TGS molecules towards the crystal surface, while in the case of {001} faces the surface diffusion mechanism of crystallization is clearly manifested. Dislocation densities in the crystals have been determined by means of etching technique. The number of dislocations increases with increasing supersaturation; hence, supersaturation of the solution together with the processes taking place in the regeneration zone surrounding the seed determine the number of dislocations in the crystal volume and thus the resulting structural perfection of single crystals. Investigation of the spontaneous redistribution of domains showed that the growth rate of TGS crystals influences the dielectric properties to much smaller extent than does chemical purity.     

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。     

Criterion for identification of ferroelectric domains in TGS crystals from AFM images

Criteria for identification of actual (dynamic) domains and morphologically similar domain “memory” regions are proposed based on the study of various types of contrast of topographic atomic-force microscopy images of lenslike regions on the polar surface of TGS crystals. Inaccuracy in identification may result in further errors in estimating the parameters of the domain structure. The images of ferroelectric domains in the spreading-resistance mode that indicate directly the presence of conductive properties of the domain walls have been obtained for the first time.     

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.     

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...     

Dielectric behaviour of TGS crystals poled by doping on repeated temperature cycling

Data characterizing the stability of basic dielectric properties against thermal treatement are presented for crystals of TGS and deuterated TGS doped with alanine or bivalent platinum. Complex permittivity and over-all polarization have been measured during a heating-cooling cycle. In alanine doped crystals the heating and cooling curves are perfectly reproducible. In Pt-doped samples the reproducibility is worse, for pure TGS the properties on cooling are strongly influenced by domain effects. These data made it possible to estimate the change of the figures of merit for pyroelectric ir detectors due to transient heating.     

Growth and Kinetic Measurements of Triglycine Sulphate Crystals

Synthesis and two-step recrystallisation have been used to produce TGS basic substance. Kinetic measurements have been performed for (110)-type face on a large scale of supersaturations up to about 3%. Evidences of impurity influence for small supersaturation and the “coverage” effect has been estimated.     

Peculiarities of the Dielectric Spectra of Triglycine Sulfate Crystals with a Profile Distribution of Chromium

Crystallography Reports - The temperature evolution of the dielectric spectra of TGS–TGS + Cr crystals (TGS stands for triglycine sulfate) with a periodic distribution of chromium impurity...     

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.     

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.     

Growth of thiourea-doped TGS crystals and their characterisation

Thiourea-doped Triglycine sulphate (ThTGS) crystal with three different concentrations of thiourea was grown from aqueous solution by slow cooling technique. The cell parameters were determined from powder X-ray diffraction analysis. A qualitative analysis of the presence of thiourea in doped crystals was estimated by FTIR analysis. Microhardness studies were carried out using Leitz Weitzler hardness tester at room temperature. Dielectric properties of the crystals were studied which showed a shift in the T_c when compared to pure TGS crystal. Pyroelectric studies were carried out and the pyroelectric coefficient was found. Piezoelectric studies (d₃₃ coefficient) has also been carried out.     

Internal bias field in triglycine sulphate crystals with <Emphasis Type="Italic">L</Emphasis>-, α-alanine grown at negative temperatures

The dielectric and pyroelectric properties of triglycine sulphate (TGS) crystals with L, α-alanine impurities grown at negative temperatures have been investigated. It is shown that a lower impurity concentration (2 mol % in solution) in this temperature range leads to the formation of internal bias fields of the same order of magnitude (∼800 V/cm) as for TGS crystals grown at T ⩽ 50°C but with an L, α-alanine concentration of 20 mol % in solution.