Investigation of the Structure of Crystal-Forming Solutions of Potassium Dihydrogen Phosphate K(H2PO4) (KDP type) on the Basis of Modeling Precursor Clusters and According to Small-Angle X-Ray Scattering Data

Crystallography Reports - The potassium dihydrogen phosphate K(H2PO4) (KDP) cluster structures formed in aqueous solutions have been theoretically and experimentally investigated. Cluster modeling...     

The Effect of Nonelectrolyte Additives with Hydrophilic and Hydrophobic Hydration on the Growth of KDP Crystals from Aqueous Solutions

Crystallography Reports - The effect of nonelectrolyte additives with hydrophilic and hydrophobic hydration on the growth of potassium dihydrogen phosphate (KH2PO) crystals in the kinetic mode at...     

磷酸盐低温烧结高强度SiC泡沫陶瓷及性能研究

通过有机模板复制法,以磷酸二氢铝为粘结剂,950 ℃烧成制备了高强度SiC泡沫陶瓷.研究了浆料中SiC含量和磷酸二氢铝含量对SiC泡沫陶瓷微观结构与性能的影响.结果表明:SiC微粉由A型Al(PO3)3粘结起来,烧成泡沫陶瓷通孔结构良好,开气孔率介于75;~91;之间.随着磷酸二氢铝含量的增加,烧成泡沫陶瓷的线收缩率、体积密度和抗折强度均逐渐增加,而开气孔率则逐渐减小;随着SiC含量的增加,烧成泡沫陶瓷的线收缩率和开气孔率均逐渐减小,而体积密度和抗折强度则逐渐增加.磷酸二氢铝含量为40;、SiC含量为60;时,泡沫陶瓷的抗折强度达(2.22±0.26) MPa.     

磷酸盐结合法制备Al2O3多孔陶瓷及性能

以煅烧α-Al2O3粉为骨料、磷酸二氢铝为高温烧成粘结剂、石蜡为成型助剂,通过模压成型、干燥、烧结等工序制备了氧化铝多孔陶瓷,研究了烧成温度和磷酸二氢铝含量对氧化铝多孔陶瓷微观形貌、物相组成、线收缩率、孔隙率和弯曲强度的影响,探讨了磷酸盐结合法烧结机理.结果表明:氧化铝多孔陶瓷物相由α-Al2 O3和AlPO4构成,在较低温度下,氧化铝颗粒仅依靠AlPO4的粘结作用而形成多孔陶瓷,氧化铝多孔陶瓷线收缩率和弯曲强度随磷酸二氢铝含量的增加而缓慢增大,孔隙率则缓慢降低;随着烧结温度的提高,AlPO4的存在促进了氧化铝颗粒间的液相烧结,线收缩率和弯曲强度随烧结温度的升高而显著增大,孔隙率也明显降低.     

溶液中结晶生长的动力学模拟:化学键合方法

基于化学键合的角度对晶体生长过程的理解,提出了一个由动力学因素控制的形貌预测模型.该模型同时考虑了晶体内部结构和环境生长因素对晶体最终形貌的影响.对磷酸二氢钾 (KDP) 和磷酸二氢铵 (ADP) 晶体在不同动力学条件下的生长形貌进行了理论模拟,所预测的结果与实验观测结果基本一致.同时比较了相同过饱和度条件下KDP和ADP晶体的生长形貌,认为晶体局部成键性质不同是导致两者形貌差异的根本原因.本文通过对动力学因素控制的生长形貌的分析,为实际晶体生长过程中的形貌调控研究及应用提供理论依据.     

Crystal and Molecular Structure of Anion Radical Salt (N-Me-DABCO)(TCNQ)2

Crystallography Reports - An anion radical salt of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with the complex composition (N–Me–DABCO)(TCNQ)2 (1) has been synthesized. The crystal...     

Effect of additives in supersaturated binary and ternary solutions on cluster growth by gravity driven concentration gradient studies

The concentration gradients formed in long column supersaturated solutions of the binary systems Potassium dihydrogen phosphate ‐ Water, Benzophenone ‐ Ethanol, Ammonium dihydrogen phosphate – Water, Potassium hydrogen phthalate – Water and ternary systems Potassium dihydrogen phosphate – Potassium chloride ‐ Water, Benzophenone – Urea ‐ Ethanol, Ammonium dihydrogen phosphate – Urea ‐ Water, Potassium hydrogen phthalate – Ethylenediaminetetraacetic acid – Water under stirred and non‐stirred conditions have been studied. The solution concentration was measured at different heights, at different degrees of supersaturation and at different times. Weight average molecular weight, Degree of Association, Number average molecular weight, Average number of molecules per cluster and weight average cluster diameter were calculated for binary and ternary supersaturated solutions under stirred and non‐stirred conditions. Under stirred conditions concentration gradient of all the above mentioned systems decrease compared to non‐stirred conditions. The cluster sizes are estimated from concentration gradient data in the presence and absence of additives and also corresponding changes in metastable zonewidths are studied. The changes in concentration gradients of supersaturated solutions appear to be a reliable indicator of the effect of additives on cluster growth and nucleation. As long column of solution is used in growing crystal by Sankaranarayanan‐Ramasamy method the effect of gravity driven concentration gradient on critical column length is investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Resonant diffraction of synchrotron radiation: New possibilities

Resonant diffraction of synchrotron radiation (SR) is a modern method of studying the structure and properties of condensed matter that can be implemented on third-generation synchrotrons. This method allows one to investigate local properties of media (including magnetic and electronic ones) and observe thermal vibrations, defects, and orbital and charge orderings. A brief review of the advance provided by SR resonant diffraction is presented, and the capabilities of this method for analyzing phase transitions are considered in more detail by the example of potassium dihydrogen phosphate and rubidium dihydrogen phosphate crystals. It is shown that the investigation of the temperature dependence of forbidden reflections not only makes it possible to observe the transition from para- to ferroelectric phase, but also gives information about the proton distribution at hydrogen bonds.     

Group-Theoretical Classification of Aristotypes of Cation and Anion Orders in Perovskites

Crystallography Reports - A group-theoretical classification of cation and anion orders of crystals with a perovskite structure is presented. Aristotypes are idealized structures (phases), from...     

Electric and Dielectric Evaluation of KDP

Single crystals of potassium dihydrogen phosphate, KH₂PO₄ (KDP), grown by isothermal evaporation at room temperature have been characterized by their measurement of electrical conductivity and dielectric behaviour. Implications in respect of practical utility of KDP crystals in devices have been given.     

Chemical bond analysis of the crystal growth of KDP and ADP

The bond valence model is employed to calculate the bond strength of constituent chemical bonds formed between growth units in both potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) crystals, with the aim to predict and control the crystal shape. After calculating and comparing the relative growth rates of all selected planes, which are related to the crystallographic structure and chemical bond strength, the natural morphology of both KDP and ADP can be conveniently deduced. To check the calculated results, the crystallites of KDP and ADP are grown under different growth conditions; their morphologies accord well with our theoretical calculations. Meanwhile, the influence of ethanol anti-solvent on crystal morphology is microscopically interpreted, which alters the crystal morphology by changing the supersaturation of the growing solution and influencing the bonding process. When ethanol is added into the growing solution, the crystal shape becomes slender.     

DKDP Crystals for Electrooptic Devices

The deuterated homologue of potassium dihydrogen phosphate crystals (DKDP) was grown by a modified transport method. Experimental results concerning electrooptic characteristics of these single crystals used in construction of a Q-switch and a four-crystals modulator are presented. An infrared extension of KURTZ -ROBINSON model electrooptic effect is also given.     

The heteroepitaxial growth of KDP/ADP

Crystal growth rules of mixture crystals KADP (potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP)) have been analyzed based on the solubility product principle. The heteroepitaxial layers have been obtained by immersing KDP (ADP) substrate into the ADP (KDP) saturated solution at 313 K. The micromorphology indicates that small growing points on different planes show the self‐similar property compared to the bulk crystal's morphology. The process of epitaxial growth depends on not only form the lattice match but also form crystallizing kinetics which is the main influencing factor. Moreover, it can infer from the micromorphology on the surface of the mixed crystal that the dissolving of substrates will form mixed solution on epitaxial surface. What's more, corrosion phenomenon gets more and more evident with increasing times of epitaxial growth and it will be harder to form transparent epitaxial layers due to the increasing tension of epitaxial layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of K1‐x(NH4)xH2PO4 mixed crystals onto z‐cut point seeds

Mixed crystals of potassium dihydrogen phosphate and ammonium dihydrogen phosphate were grown onto point seeds by the method of temperature reduction. It was found that the regeneration process of z‐cut point seeds became more and more difficult with increasing KH₂PO₄ concentration in the solution mixture. The interior stress and cracking of the mixed crystals were analyzed by synchrotron X‐ray topography. Large numbers of stress stripes were found at the seed and sectors boundaries. The lattice parameters of the pyramid and prismatic sectors of the prepared mixed crystal were calculated according to the X‐ray diffraction patterns. With solution containing 8 mol % KH₂PO₄, the lattice volumes of the prismatic sector of the mixed crystal were 1.3% larger than that of the pyramid sector of the crystal. Chemical etching revealed microcracks with length of hundreds of microns in the mixed crystals, which tended to spread and led to crystal cracking. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlations of Anion Size and Symmetry with the Structure and Electronic Properties of β-(BEDTTTF)2X Conducting Salts with Trihalide Anions X = 13-, 12Br-, 1Br2-

In the isostructural series of β-(BEDT-TTF)₂X organic metals, abbreviated β-(ET)₂X, where X is a trihalide anion, I₃-, I₂Br- or IBr₂-, and where ET is bis-(ethylenedithio) tetrathiafulvalene (C₁₀S₈H₈), the salt containing the disordered asymmetric I₂Br- anion has atypical structural and electronic properties compared to those containing the symmetrical and ordered I-₃ and IBr₂- anions.     

Growth and thermal studies on pure ADP,KDP and mixed K1‐x(NH4)xH2PO4 crystals

The investigations on the formation of mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP) i.e. potassium ammonium dihydrogen phosphate, K_1‐x(NH₄)_xH₂PO₄ have been presented in this paper. Pure and mixed crystals of ADP and KDP have been grown by slow evaporation technique from the supersaturated solution at an ambient temperature 26±1 °C for ammonium concentration x in the range 0.0 ≤ x ≤ 1.0 in the case of mixed crystals. Crystal compositions were determined by flame atomic absorption spectroscopy and chemical analysis. The results of the X‐ray analysis of the grown crystals are also reported. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the kinetic process of dehydration and the high temperature phase behaviour. DTA showed the distinct thermal events attributed to dehydration of ADP, KDP and K_1‐x(NH₄)_xH₂PO₄. The results of thermal analysis and chemical analysis are consistent with each other. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the transport processes in tetramethoxysilane gel by the moiré fringes method

Moiré fringes method have been used in order to study the mass transport processes in tetramethoxysilane (TMS) gel in respect of crystal growth experiments. Diffusion coefficients of potassium dihydrogen phosphate (KDP) solution and ethanol in pure and soaked TMS gel have been measured.     

Dielectric properties of rapidly grown KDP crystals

The dielectric properties of rapidly grown potassium dihydrogen phosphate KH₂PO₄ (KDP) crystals have been studied over a wide temperature range and compared with the properties of traditionally grown KDP crystals. It was found that the contribution of domains to permittivity in rapidly grown crystals is considerably less than in conventionally grown ones. The dielectric properties in various growth sectors of KDP crystals are determined.     

The role of hydrodynamics and supersaturation in the formation of liquid inclusions in KDP

The formation of liquid inclusions in large potassium dihydrogen phosphate crystals is a result of depletion in stable eddies formed at the rear (downstream) faces. A large concentration jump can be expected at the point where the “exhausted” fluid meets the fresh liquid. The response of a step train on a jump in supersaturation has been investigated by means of computer simulations. The results are in good agreement with the experiments.     

Effect of strain in crystal on the forbidden reflections in the resonant diffraction of synchrotron radiation

The effect of strain (either static or caused by long-wavelength acoustic oscillations) on the energy spectrum and the azimuthal dependence of the intensity of “forbidden” reflections in crystals at the energy of incident radiation close to the absorption edge is considered. It is shown that a strain causing a weak change in the unit-cell symmetry may additionally contribute to the tensor atomic factor. Examples of changes in the azimuthal dependence of forbidden-reflection intensity in zinc oxide ZnO and potassium dihydrogen phosphate KH₂PO₄ are considered.