摘要:

AbstractIn separation processes containing solids, mostly crystals, the interest in shape modifications of the solids has increased. The idea in it is the necessity to save energy, to achieve specific product requirements, e.g. purities, or to provide downstream processes with better feed material. For an organic crystal a simple way to select a growth inhibitor is presented here, in contrast to the concept of “tailor‐made additives”. The additive selected is structurally different from the host molecule and modifies the habit in a desired manner. The procedure of additive selection involves the analysis of the molecular structure of the crystal to be modified and the orientation of the molecules at the surfaces of the morphological most important faces. Furthermore the problem is discussed if the chosen additive is incorporated into the crystal or not. Results are shown for the system caprolactam/et

ISSN:0232-1300    

DOI:10.1002/crat.2170300319

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170300320

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe growth of facets and the generation of twins onVGF (vertical gradient freeze technique) grown GaAs were investigated using DSL (diluted Sirtl‐like etchant with light) photoetching and transmission X‐ray topography. Due to the polarity of the (111) plane in GaAs, As facets are larger and more irregular than Ga facets and twins always occur on As facets. Twins are initiated at the change of boundary condition which is affected by temperature gradient and crucible shape. The mechanism of twin generation is explained by considering the edge concavity at the solid‐liquid interface and the supercooling required for initial nucleation of a facet. Twins are more often produced in Si‐doped crystals than undoped ones due to the constitutional super

ISSN:0232-1300    

DOI:10.1002/crat.2170300321

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170300322

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe paper is the third in a series which presents results on the small‐signal diametral response of a Czochralski crystal grown in a resistively heated furnace to variations in heater temperature and pull rate. For typical growth conditions and a wide range of materials it has been shown that this response is obtained by solving a set of linear differential equations. Conditions for normal response, i.e. the diameter increasing on heater temperature and/or pull rate decrease, have been established and shown to hold for most practical cases. The transfer function obtained is consistent with previous results for an inductively heated growth apparatu

ISSN:0232-1300    

DOI:10.1002/crat.2170300323

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractSamples with the nominal composition Bi2Sr2Ca1–xLixCu2Oy(x= 0.2,0.4, and 0.6) and Bi2Sr2CaCu2−xL1xOz(x= 0.4, 0.6, and 1.0) were prepared by the solid state reaction method. The role of L1 at both Ca and Cu sites in the Bi‐2212 composition were studied. From the X‐ray diffraction data it was found that the L1‐doped at the Ca site increases thec‐axis and that doped at the Cu site decreases thec‐axis. From the D.C. four‐probe resistivity data it was found that Li‐doped at the Ca site reduces theTcand the L1‐doped at the Cu site givesTc(0) above the liquid nitrogen temperature. It was observed that the L1 doping reduces the melting point of Bi‐2212 composition. The presence of Lithium was confirmed by inductive the

ISSN:0232-1300    

DOI:10.1002/crat.2170300324

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of ultraviolet radiation on the nucleating behaviour of AgI, AgCI, AgI–AgCI–CuI system in pure water has been discussed. Also the effect of irradiated AgI—AgCI—CuI samples in the presence of chlorides of sodium, potassium, and ammonium as well as sulphates of sodium, ammonium, and magnesium has been reported. The UV exposed samples of AgI and AgCI become darkened and their nucleating activity is found to be greatly reduced as the time of exposure is increased. It is found that the exposure of the AgI—AgCI—CuI samples to ultra‐violet radiation does not produce a remarkable effect in nucleation activity, except, the samples becoming dark for longer exp

ISSN:0232-1300    

DOI:10.1002/crat.2170300325

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractSingle crystals of pure and monovalent metallic ion doped (K+, Na+, Cu+, Ag+, and Hg+) lead(II)chloride and lead(II)bromide were grown using silica gel. The growth experiments have been carried out by employing a modified two‐stage chemical reaction. The grown crystals of pure and doped lead(II)chloride and lead(II)bromide are subjected to microhardness studies. The validity of Kick's relation is checked. The value of standard hardness numberHvand the work hardening coefficientnare found out. The influence of the presence of the added dopant on the microhardness behaviour of the crystal is studied. A possible relation between the hardness valueHvand the ionic radii of the added dopants is established and the results are discusse

ISSN:0232-1300    

DOI:10.1002/crat.2170300326

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPraseodymium‐doped GaAs and Al0.3Ga0.7As epilayers grown on Semi‐Insulating (SI) GaAs substrates by Liquid Phase Epitaxy (LPE) were first studied in this present work. Measurement techniques, such as microscopic observation, X‐ray diffraction, Secondary Ion Mass Spectroscopy (SIMS), and Hall measurement were employed. Layers doped with Pr resulted in a mirror‐like surface, except several high Pr‐doped layers having droplet surfaces. Hall measurements reveal that the grown layers contained p‐type layers, carrier concentrations from 6.3 × 1015to 1.2 × 1016cm−3, and from 6.3 × 1015to 3.5 × 1016cm−3for Pr‐doped GaAs and Al0.3Ga0.7As epilayers, respectively. Although p‐type conduction exists, in the light of electrical features, doping of Pr into the GaAs and Al0.3Ga0.7As growth melts, is still considered to exhibit gettering properties rather than to become a new acceptor itself. Additional photoluminescence examinations were taken. Their results also indicate that Pr‐doped layers produce no new emission lines and support th

ISSN:0232-1300    

DOI:10.1002/crat.2170300327

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170300301

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY