Anisotropy of microhardness and fracture in Cs2Ni(SO4)2 · 6H2O single crystals

The microhardness of the (010), (100), and (001) planes in the Cs₂Ni(SO₄)₂ · 6H₂O crystal and the geometry of destruction of the (010) plane around impressions of different (spherical, Vickers, and Knoop) indenters has been studied using Vickers indentation. It is shown that the crystal under study is characterized by enhanced brittleness and that the cleavage along the (201) plane is highly imperfect. The maximum microhardness (H = 1140 MPa) is characteristic of the (001) plane under a load of 20 g.     

Evidence of slip in calcium fluoride single crystals

Natural single crystals of calcium fluoride have been cleaved along (111) planes and the cleavage faces have been etched in 0.2 N nitric acid solution. Etching produces rows of equally spaced etch pits running in <110>directions. One-to-one correspondence of glide bands has been established on the matched faces and on the three different flakes of the same crystal. This is further confirmed by studying the rosette structure produced on a (111) cleavage plane by indenting that plane itself. The active slip planes are found to be {110}. The implications are discussed.     

Vickers microhardness of K<Subscript>2</Subscript>Co(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O single crystals and fracture geometry around impressions of vickers,knoop, and spherical indenters

The microhardness on the (010) and (001) planes in K₂Co(SO₄)₂ · 6H₂O crystal has been measured by the Vickers indentation method. Its values are, respectively, 11500 and 1300 MPa. No microhardness anisotropy of the first kind is revealed on either plane. The fracture geometry under indentation by a spherical indenter and Vickers and Knoop indenters is studied. The crystal has lower brittleness than the isomorphic Cs₂Ni(SO₄)₂ · 6H₂O crystal.     

Anisotropy of Microhardness and Fracture of Langasite Crystal and Its Structural Basis

Crystallography Reports - The anisotropy of microhardness and fracture of the (0001) basal plane of langasite crystal has been studied using Berkovich indentation under a load of 100 g at different...     

Growth of YBa2Cu3O7 films with [110] tilt of CuO planes to surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with the CuO plane tilted to the surface have been grown on SrTiO₃ crystalline substrates by pulsed laser deposition. This tilt was obtained by rotating the film lattice with respect to the substrate surface around its [110] axis oriented parallel to the surface. The zero tilt of the CuO plane was implemented at the orientation of the SrTiO₃ crystal surface parallel to the (100) plane. The rotation angles were varied in the range from 0° to 70°. It is found that, being tilted at any angle, the CuO planes of the film remain parallel to one or several crystallographic planes of the (100)-type substrate. In the range of tilt angles from 0° to 49°, the film has a single-crystal structure. Above 49° the film is transformed into a three-domain texture and its surface roughness sharply increases.     

Athermal Directions in KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> Crystal

All orientations of the phase normal, at which the phase of a light wave propagating through a crystal is independent of its temperature (athermal phase directions), have been numerically found for a KGd(WO₄)₂ crystal. There are two sets of such directions for each isonormal wave. Their intersection with the main planes of the optical indicatrix of the crystal yields four athermal directions in the planes orthogonal to the axes with the minimum and intermediate refractive indices and two directions in the plane orthogonal to the axis with the maximum refractive index.     

Anisotropy of microhardness and fracture of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Ni(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O (ANSH) crystals

The Vickers hardness of the (010) and (001) planes in (NH₄)₂Ni(SO₄)₂ · 6H₂O (ANSH) crystals has been measured. Anisotropy hardness of the first kind is revealed for the (010) plane in ANSH. The hardness anisotropy coefficient k ₂ was determined to be 1.5. The temperature dependence of the microhardness of the (001) face of ANSH crystals was investigated in the temperature range from 20 to 80°C. The character of fracture of the (100), (010), and (001) planes during indentation with a spherical indenter has been qualitatively determined.     

Anisotropy of microhardness of β-BaB2O4 single crystals

The anisotropy of microhardness of β-barium borate single crystals β-BaB₂O₄ (BBO) is studied by the sclerometry method on the (0001) basal plane, the $(10\bar 10)$ plane of the hexagonal prism, and the $(11\bar 20)$ plane of the trigonal prism. It is shown that the anisotropy observed in the crystal is determined by the directions of covalent B-O bonds. It is established that the anisotropy of microhardness correlates with the system of cleavage planes.     

Crystal growth,thermal, optical and microhardness studies of tris (thiourea) zinc sulphate - a semiorganic NLO material

Tris (thiourea) zinc sulphate (ZTS), a semiorganic nonlinear optical (NLO) material has been synthesized at 30 °C. The solubility was determined in different solvents such as water, ethanol and water mixture of ethanol (1:1). Good quality single crystals with size 10 × 8 × 6 mm³ were grown by slow evaporation technique within three weeks with approximate growth rate of 0.5 mm/day. The grown crystals have been subjected to single crystal X-ray diffraction to determine the unit cell dimensions and morphology. The TGA and DTA reveal that the material has good thermal stability. The UV-Vis spectrum shows that the material has wide optical transparency in the entire visible region. The second harmonic generation was confirmed by Kurtz powder method. The birefringence of the crystal was measured in the visible region and it was found to vary with the wavelength. The microhardness test was carried out in (100) plane and the load dependent hardness was measured. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the Mechanical Properties of TbF<Subscript>3</Subscript> Crystals

TbF₃ (sp. gr. Pnma) crystals up to 40 mm in diameter have been grown from melt by a Bridgman technique. The anisotropy of their mechanical properties is studied for the first time. the technical elasticity constants are calculated, and room-temperature values of Vickers microhardness for the (010) and (100) planes are measured. The shape of indentation impressions is found to correlate with Young’s modulus anisotropy for TbF₃ crystals.     

Single crystal growth,structural, optical,mechanical, dielectric and thermal studies of formic acid doped potassium dihydrogen phosphate crystal for NLO applications

Optically transparent formic acid (FA) doped potassium dihydrogen phosphate (KDP) crystal of dimension 21×15×9 mm³ has been grown by slow evaporation solution technique (SEST). The X‐ray diffraction (XRD) technique was used to confirm the cell parameters and the shifts in peak positions of identified reflecting planes. The incorporation of FA in KDP has been qualitatively analyzed by fourier transform infrared analysis. The UV‐visible absorption spectrum of crystals has been recorded in the range of 200 to 900 nm and the doped KDP crystal is found to have improved optical parameters than pure KDP. The color centered photoluminescence emission spectrum of grown crystal has been illustrated in visible region. The mechanical behavior of pure and doped KDP crystal has been investigated using the Vicker's microhardness analyzer and hardness parameters have been calculated. The effect of FA on thermal stability of KDP crystal was examined by means of thermogravimetric and differential thermal analysis. The temperature dependent dielectric behavior of crystals was studied.     

Deformation and microhardness studies on natural apophyllite crystals

Microhardness testing of three different planes of natural apophyllite crystals is reported. Variation of Vicker's microhardness value H_v with applied load ranging from 10–100 g indicates two distinct regions. In the low load region (10–70 g) H_v increases with load till it attains maximum value and then decreases thereafter. This variation is explained qualitatively in terms of depth of penetration of the indentor. Variation of orientation of the indentor w.r.t. each of the (100) and (111) planes indicates microhardness anisotropy.     

Etching of GaP surfaces in Aqua regia and in the Bromine-methanol-water system

The etchants aqua regia and bromine in methanol in water and in methanol water mixtures were tested on GaP. Aqua regia acted as nonpreferential etchant on (111) B and on {100} planes, the (111) A plane proved to be more resistent to chemical attack. Indications to the formation of a protecting layer was found. Bromine in methanol proved to be preferential etchant for the {100} plane producing a surface geometry characteristic to kinetically determined processes. Increasing the amount of water the (111) B plane could be dissolved also and etch figures characteristic to nonpreferential dissolution began to appear on the {100} and (111) B planes as well. The preferential effect for the {100} plane seems to be related to the water content of the solvent.     

Domain structure in main crystallographic planes of orthoferrites at spin reorientation

The behaviour peculiarities of the domain structure of the single crystal samarium-terbium-erbium and samarium-terbium-thulium orthoferrites in the spin reorientation range in three crystallographic planes (001), (110) and (100) are investigated. In the (001)-plane the temperature-induced bubble domain lattice formation is observed. The formation kinetics of these domains is similar to the process of nucleation and that of growth with spontaneous crystallization. In the (110) plane the inclined domains formation is noted. The canting angle depends on temperature at spin reorientation. The values of remagnetization fields are measured as a function of temperature in the indicated crystallographic planes. From the measured changes of the domain structure the temperature dependences of the first anisotropy constant and the domain wall density are determined.     

Growth and some properties of TeO<Subscript>2</Subscript> single crystals with a large diameter

Large-diameter single crystals of TeO₂ are grown by the Czochralski method in specially designed setups with automatic monitoring of the crystal growth. The degree of perfection of the grown crystals is examined using selective etching and X-ray topography (the Shultz method). The temperature dependence of the microhardness of TeO₂ single crystals is investigated for different crystallographic planes, namely, (001), (100), and (110).     

Deformation and microhardness studies on KClO4 single crystals

The deformation characteristics of KClO₄ single crystals have been studied by the methods of static and dynamic indentation on (001) plane. The cracks produced by the dynamic indentation have been interpreted in terms of slip-twin interactions. Also, the load dependence of Vickers microhardness and its anisotropy in this crystal are reported. The observed hardness anisotropy has been used to confirm the indices of the slip system 〈101〉 〈111〉 operative in this crystal at ordinary temperatures.     

Growth mechanism, dislocation etching and mechanical properties of L-arginine phosphate and deuterated L-arginine phosphate

Single crystals of L-arginine phosphate monohydrate (LAP) and its deuterated analog (dLAP) were grown from aqueous solutions. Effect of pH variation on growth of microbes in these solutions was studied. Efforts were undertaken to minimize microbial incorporation into these crystals. The grown crystals were characterized by recording the powder diffraction and identifying the diffracting planes. Dislocation contents of these crystals were estimated by etching the cleavage planes using a mixture of glacial acetic and ethanol. Growth features on habit faces of LAP and dLAP were studied. Growth takes place on the (100) plane predominantly by spreading of layers which manifests as a step pattern. Hillocks were observed on (0 0), (1 0 and ( 10) habits faces. Load dependence of microhardness was evaluated for LAP and dLAP.     

Magnetostimulated changes of microhardness in potassium acid phthalate crystals

A decrease in microhardness along the (010) cleavage in potassium acid phthalate single crystals by 15–18% after the application of a permanent magnetic field is revealed for the first time. It is shown that the effect revealed is of the volume character. The role of interlayer water in the processes stimulated by a magnetic field is studied. Interlayer water does not cause the observed changes; it only plays the part of an indicator of these changes in potassium acid phthalate crystals in a magnetic field. It is established that microhardness in the (100) plane of the crystal in an applied a magnetic field first increases by 12–15% and then remains constant in time within the accuracy of the experiment. The possibility of varying the crystal structure of potassium acid phthalate crystals by applying magnetic fields inducing rearrangement in the system of hydrogen bonds or in the defect structure is discussed.     

Microhardness investigations on potassium dihydrogen phosphate crystals

Vickers microhardness measurements are carried out on single crystals of potassium dihydrogen phosphate. Dependence of hardness on indentation load and anisotropy in hardness of (100) and (011) planes are described. Crack patterns around indentation are found to be dependent on indenter orientation. Also explained are the fracture at high indentation load and etch patterns obtained on indented surfaces.     

富硼体系中立方氮化硼晶体的生长

本文在hBN-Li3N体系中添加不同含量的单质硼(B),研究了cBN晶体在富B条件下的生长特性.结果表明,B进入晶体的位置具有明显的区域选择性.B以占据N(111)面内N空位的方式进入晶体,并与原有的N原子一起形成一个B原子和N原子的(111)面.随着B进入量的增加,越来越多的B原子取代N空位,B和N原子的混合面与邻近的B(111)面叠加,在晶体的中心部位形成颜色较深的三角形阴影并逐步扩展,最后,使晶体完全变成黑色.由于B占据N空位造成原来N的(111)面上有大量硼原子存在,使得晶体沿＜111＞方向生长困难而有利于沿＜100＞方向生长, 从而形成了八面体或类球形晶体.同时,由于加入的B与部分Li3N发生化学反应也可生成cBN,因此,体系中cBN晶体的形成受两种机制控制:一种为溶解析出过程,另一种为化学反应过程.cBN的产率随着B添加量的增加而降低的实验结果表明,溶解析出过程占主导地位.