CsCl-NaCl system

According to these analyses of a molten CsCl-NaCl system, the averaged coordination number and the interionic distance for a Na-Cl pair were determined to be about 4.4 and 0.29 nm, respectively, those for Cs-Cl being around 4.3 and 0.34 nm. These values were almost comparable to those estimated in each pure melt by XRD [24,25], MD [26-29], and ND [30,31], indicating that the short-range structure of the Cs or Na neighborhood in a molten CsCl-NaCI system was maintained in about the same manner as it was in each pure melt. 

Pniim-Fniim transformations of solid solutions of CsCl with KC1 and CsBr exhibit different behaviours. With increasing percentages of KC1, the NaCl structure gets stabilized in the CsCl+KCl system. In the CsCl+CsBr system, the transformation temperature increases with % CsBr and AH essentially remains constant. Both these behaviours can be satisfactorily explained in terms of the Born treatment of ionic solids. The Pmlm-Fniim transformation retains its first-order characteristics in the CsCl+KCl system, but higher-order components seem to be present in the CsCl+CsBr system. Incorporation of vacancies do not affect the transformation of CsCl markedly. 

V.L. Cherginets and T.P. Rebrova, Solubility of Magnesium Oxide in Eutectic Melts of KCl-LiCl and CsCl-KCl-NaCl Systems, Zh. Neorg. Khim. 49 (2004) 1571-1574. 

We will first discuss XSR studies on compounds of the form MX (where M is a R or An and X either a pnictide, a chalcogenide, or a noble metal), which crystallize either in the NaCl or CsCl cubic structures. This will be followed by an overview of (xSR results in MX3 compounds crystallizing in the cubic AuCus structure. Most xSR data are available for the NaCl systems. The An materials are restricted to U compounds. 

Fig.lb are expressed relative to the relatively narrow signal of NbClj in CsCl/NaCl(eut) at 425°C, since all reference systems described in literature like NbCls in acetonitril [13] are not suitable here. 

SOLID AND LIQUID NbClj-MCl-M Cl-MIXTURES For the investigation of NbCls in alkali halide melts low melting eutectic mixtures have been selected due to the corrosivity of NbCls at temperatures above 600 °C. Mixtures of interest are CsCl/NaCl (Tgut=490 °C) and LiCl/KCl (Teut = 375 °C). In these two systems studies of the electrochemical reduction mechanism of Ta(V) and Nb(V) have recently been performed in our group [5,20]. The phase diagrams of these ternary systems are not reported in literature, only the binary mixtures have been measured up to now [21,22,23]. Fig.3 shows the phase diagram of the pseudo binary system NbCls-CsCl/NaCl (eut) up to a concentration of x =0.45 as measured with... 

DTA. These measurements have been limited to temperatures below 600 °C. A characteristic of this system is the solid-solid transition at 295 C. High and low temperature solid state modifications are also reported for the binary systems NbClj in CsCl, NaCl and KCl. NaNbCl and KNbCl reveal a structure consisting of dimers in the low temperature modification comparable to NbCls. CsNbClg is a stable, congraent melting compound and consists already in the low temperature modification of NbCl units. 

The striking effect of the alkali metal cation on the physical properties of mixed melts of this sort is shown particularly well in a comparison of the PbCla-KCl and PbCl-s-NaCl systems. As described by Bloom (1959), the latter shows a simple phase eutectic, only slight deviations in the equivalent conductivity and activation energy (negative and positive, respectively), linear molar volumes, and PbCh and NaCl activities which deviate little from ideality. The surface tensions of the PbCh-MCl systems regularly change from a linear relationship with LiCl to an even deeper minimum than illustrated in Fig. 3 (c) for CsCl. 

We have studied the transformations of the CsCl + KCl and CsCl + CsBr solid solutions in order to find the limitations and applicability of the Born treatment in explaining the two entirely different behaviours of the solid solutions of these two systems. Such a study is of value since theoretical approaches to explain the relative stabilities of structures of ionic solids have not been quite successful, and it is important to explain the relative stabilities of at least the two simplest structure types in ionic solids, viz., the NaCl and CsCl structures. We also wished to find out whether the first order characteristics of Pm3m-Fm3m transitions are retained in the solid solutions. We have therefore examined the crystallography of the Pm3m and Fm3m phases of the solid solutions as functions of temperature from these data, coefficients of expansion of the two structures have been calculated. 

In the systems LiCl-TiCU, NaCl-TiCb, and RbCl-TiCb, no compounds are formed, while in the systems KCl-TiCb and CsCl-TiCb, the congruently melting compounds K2TiCl6 and Cs2TiCl6 originate respectively. 

Perhaps the majority of systems which are known are found in the. .. ABAB... arrangement. This includes the well known ZnS, NaCl and CsCl structure types and almost certainly occurs as a result of the fact that many stable systems occur when the collection of bonding orbitals are occupied but the corresponding antibonding orbital collection is empty. Such a situation often corresponds to a half-filled band (x = 0.5).. .. AABB.,. stackings are usually regarded as somewhat unusual by comparison. For example, note the ZrCl structure with its proximal layers of metal atoms. 

Polythermal investigations of equilibrium (1.2.3) in the molten CsCl-KCl-NaCl eutectics (600, 700, and 800 °C) and KCl-NaCl eutectics (700 and 800 °C), and in an individual KC1 melt at 800 °C were reported in Ref. [313]. These studies were performed by consecutive calibration of the electrode system with addition of a strong Lux base in an argon atmosphere and in pure C02, as shown in Fig. 2.5.7. The data show that passing C02 through the melts causes a considerable increase in e.m.f. This means a considerable reduction of the equilibrium O2- concentration owing to its fixation by C02 followed by the formation of carbonate. From the known slope of the calibration -pO dependence one can estimate the pK value using the formula presented in Fig. 2.5.7. The equilibrium molality of... 

Lack of perfection is apparent even in the results for the 1 1 salts. Although the parameters show significant regularity, they do not satisfy additivity relations within the fitting error. Letting q stand for the characteristic ion size or hydration number of an electrolyte, relations such as q(KBr) = q(KCl) -I- q(NaBr) - q(NaCl) should be satisfied. For KBr, we predict values of 7.27 and 1.98 for the ion size and hydration number the fitted values are 7.14 and 1.53. Although this is not too bad, if we attempt to predict the same parameters for CsBr from those of CsCl, NaBr, and NaCl, we obtain 5.25 and 1.75, compared to fitted values of 4.20 and 1.14. One could go further and test the ability of the models for pure aqueous electrolytes to be extrapolated to predict the properties of mixtures, such as the system NaCl-KCl-H20, as no additional fit parameters are required by the model. However, because the additivity relations are not precisely satisfied, there seems little point in doing so. 

This paper reports an extensive study of the Th-Te system. The ThTe, ThTc2, ThTczee, and ThOTe phases were prepared and identified from X-ray and chemical analyses. ThTe is simple cubic with the CsCl-type stincture (unlike ThS and ThSe, which have the NaCl stincture) while ThOTe is tetragonal, isostinctural with ThOSe and ThOS. The tellurides are all degraded well below 1273 K when heated in vacuo. The Th-Te system is not analogous to the Th-S and the Th-Se systems. 

To compare the experimental lattice parameter more conveniently with the quantum-mechanical and also the classically derived ones, these are all found together in Table 3.1. Indeed, all of them agree, with respect to the [NaCl]-type lattice parameter, to lie around 4.81 A. The best value is the one derived from the empirical ionic radii but it may be argued that the latter data were, in fact, fitted to match the experimental crystal-structure results. The GGA result further allows us to estimate the classical predictions for the h)q5othetical lattice parameters of the [ZnS]/[CsCl] types, and here the fit is acceptable, too, for [ZnS] (fl 5.2 A) and [CsCl] a 3.0 A), with the only exception for the volume-increment method, in particular the [ZnS] entry. Obviously, we have already gone beyond the limits of this simplistic method and will therefore not consider it any further for the present system. 

Heats of mixing of solid solutions of CsCl with CsBr, KCl, and RbQ have been obtained by precise aqueous solution calorimetry. Results show evidence for the abrupt stabilization of the NaCl (Fm3m) structiure with respect to the CsQ (Pw3m) structure in the Csi K Cl and Csi- Rb Q systems at molar ratios corresponding to x=0.25 (Csi K,Cl) and x = 0.50 (Csi, Rb,Cl). ... 

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