Phase diagram and electrical conductivity of TbBr3-NaBr binary system

Several experimental techniques were used to characterise the physicochemical properties of the TbBr₃-NaBr system. The phase diagram determined by DSC, exhibits an eutectic and a Na₃TbBr₆ stoichiometric compound that decomposes peritectically (759 K) shortly after a solid-solid phase transition (745 K). The eutectic composition, x(TbBr₃)=39.5 mol%, was obtained from the Tamman method. This mixture melts at 699 K. With the corresponding enthalpy of about 16.1 kJ mol^-1. Diffuse reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) confirmed the existence of new phase exhibiting its own spectral characteristics, which may be possibly related to the formation of Na₃TbBr₆ in this system. Additionally, the electrical conductivity of TbBr₃-NaBr liquid mixtures was measured down to temperatures below solidification over the whole composition range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diagrammes de phases des systemes binaires KNO3-CsNO3 et KNO3-NaNO3

(K?Na)NO₃ and (K?Cs)NO₃ phase diagrams were drawn using a simultaneous thermal analysis technique in the range 373 to 623 K. The first phase diagram shows a minimum freezing equimolar mixture at 494 K, a continuous solid solution in equilibrum with liquid phase and an eutectic mixture (88 molar % of KNO₃) at 380 K. The second one exhibits an invariant at 400 K corresponding to the KNO₃ solid-solid transition, an eutectoid mixture at 10 molar % of KNO₃ and 418 K involving the CsNO₃ solid-solid transition and an eutectic mixture at 60 molar % of KNO₃ and 495 K.     

Enthalpy of Phase Transitions and Heat Capacity of Stoichiometric Compounds in LaBr3-MBr Systems (M=K,Rb, Cs)

Molar enthalpies of solid-solid and solid-liquid phase transitions of the LaBr₃, K₂LaBr₅, Rb₂LaBr₅, Rb₃LaBr₆ and Cs₃LaBr₆ compounds were determined by differential scanning calorimetry. K₂LaBr₅ and Rb₂LaBr₅ exist at ambient temperature and melt congruently at 875 and 864 K, respectively, with corresponding enthalpies of 81.5 and 77.2 kJ mol^-1. Rb₃LaBr₆ and Cs₃LaBr₆ are the only 3:1 compounds existing in the investigated systems. The first one forms from RbBr and Rb₂LaBr₅ at 700 K with an enthalpy of 44.0 kJ mol^-1 and melts congruently at 940 K with an enthalpy of 46.7 kJ mol^-1. The second one exists at room temperature, undergoes a solid-solid phase transition at 725 K with an enthalpy of 9.0 kJ mol^-1 and melts congruently at 1013 K with an enthalpy of 57.6 kJ mol^-1. Two other compounds existing in the CsBr-based systems (Cs₂LaBr₅ and CsLa₂Br₇) decompose peritectically at 765 and 828 K, respectively. The heat capacities of the above compounds in the solid as well as in the liquid phase were determined by differential scanning calorimetry. A special method - 'step method' developed by SETARAM was applied in these measurements. The heat capacity experimental data were fitted by a polynomial temperature dependence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

Study of the NaBr–DyBr3 phase diagram by differential thermal analysis

The phase diagram of the quasi binary NaBr–DyBr₃ system was determined by differential thermal analysis (DTA) applied to 27 samples covering the complete composition range of the system. The 3NaBr*DyBr₃(s) compound is present in the solid-phase in addition to the pure component halides NaBr(s) and DyBr₃(s). The DyBr₃(s) and 3NaBr*DyBr₃(s) phases showed a polymorphic transition at 1112 and at 733 K, respectively. The {DyBr₃(s) + 3NaBr*DyBr₃(s)} eutectic mixture melts at 709 K giving a liquid of the molar composition x(NaBr) = 0.62. The 3NaBr*DyBr₃(s) phase melts peritectically at 765 K. The phase diagram obtained in the present study virtually agrees with the calculated one available in literature.     

Thermodynamic and transport properties of the DyBr3–NaBr binary system

Phase equilibria in the DyBr₃–NaBr binary system were established from differential scanning calorimetry. This system exhibits incongruently melting compound Na₃DyBr₆ and one eutectic located at DyBr₃ molar fraction x = 0.409 (T = 711 K). Na₃DyBr₆ undergoes a solid–solid phase transition at 740 K and melts incongruently at 762 K. The specific conductivity of DyBr₃–NaBr liquid mixtures was measured over the whole composition range. Results obtained are discussed in term of possible complex formation.     

Effect of Nonmagnetic Substitution on the Magnetic Properties and Charge-Transfer Phase Transition of an Iron Mixed-Valence Complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)] (dto = C(2)O(2)S(2))

The iron mixed-valence complex (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)] exhibits a novel type of phase transition called charge-transfer phase transition (CTPT), where the thermally induced electron transfer between Fe(II) and Fe(III) occurs reversibly at ～120 K, in addition to the ferromagnetic phase transition at T(C) = 7 K. To investigate the mechanism of the CTPT, we have synthesized a series of magnetically diluted complexes (n-C(3)H(7))(4)N[Fe(II)(1-x)Zn(II)(x)Fe(III)(dto)(3)] (dto = C(2)O(2)S(2); x = 0-1), and carried out magnetic susceptibility and dielectric constant measurements and (57)Fe M?ssbauer spectroscopy. With increasing Zn(II) concentration (x), the CTPT is gradually suppressed and disappears at x ≈ 0.13. On the other hand, the ferromagnetic transition temperature (T(C)) is initially enhanced from 7 K to 12 K between x = 0.00 and 0.05, despite the nonmagnetic nature of Zn(II) ions, and then it decreases monotonically from 12 K to 3 K with increasing Zn(II) concentration. This anomalous dependence of T(C) on Zn(II) concentration is related to a change in the spin configuration of the ferromagnetic state caused by the partial suppression of the CTPT.     

Structural chemistry of A3CuBO6 (A = Ca, Sr; B = Mn, Ru, Ir) as a function of temperature

Variable temperature X-ray and neutron powder diffraction techniques have been used to identify structural phase transitions in Cu-rich A(3)A'BO(6) phases. A transition from monoclinic to rhombohedral symmetry was observed by X-ray diffraction between 700 and 500 K in Sr(3)Cu(1-x)M(x)IrO(6) (M = Ni, Zn; 0 < or = x < or = 0.5). The temperature of the phase change decreased in a linear manner with Cu-content and was essentially independent of the nature of M. Ca(3.1)Cu(0.9)MnO(6) was shown to pass from a rhombohedral phase to a triclinic phase on cooling below 290 K; the structure of the triclinic phase was refined against neutron diffraction data collected at 2 K. Ca(3.1)Cu(0.9)RuO(6) undergoes a transition between a disordered rhombohedral phase and an ordered monoclinic phase when cooled below 623 K. Neutron diffraction has been used to determine the structure as a function of temperature in the range 523 < or =T/K < or = 723 and hence to determine an order parameter for the low temperature phase; the second-order transition is shown to be incomplete 100 K below the critical temperature.     

四氯合锌酸十六烷基铵-四氯合锌酸十八烷基铵二元体系亚固相相图

合成了具有层状结构的热致相变材料四氯合锌酸十六铵(n-C16H33NH3)2ZnCl4,C16Zn)和四氯合锌酸十八铵(n-C18H37NH3)2ZnCl4,C18Zn)(在340~370 K的温度范围内存在着焓值较大的可逆固-固相变)。 并将此2种材料在乙醇溶液中结晶出一系列二元体系。 对二元体系利用差热分析(DTA)和X射线衍射技术进行测定,构筑了C16ZnC18Zn二元体系亚固相相图。 根据相图,确定了w(C16Zn)=41.11%处有中间化合物(n-C16H33NH3)(n-C18H37NH3)ZnCl4的存在,并测定在w(C16Zn)=16.19%和w(C16Zn)=63.07% 2处存在着2个不变的共析点,2个共析点温度分别约为356和353 K。 与同类体系的其它相图相比,在此相图的左右边界存在端际固溶体（α和β）和中间区域存在非化学计量相（γ）。     

Phase changes in Lennard-Jones mixed clusters with composition Ar(n)Xe(6-n) (n=0,1,2)

We have carried out parallel tempering Monte Carlo calculations on the binary six-atom mixed Lennard-Jones clusters, Ar(n)Xe(6-n) (n=0,1,2). We have looked at the classical configurational heat capacity C(V)(T) as a probe of phase behavior. All three clusters show a feature in the heat capacity in the region of 15-20 K. The Ar(2)Xe(4) cluster exhibits a further peak in the heat capacity near 7 K. We have also investigated dynamical properties of the Ar(2)Xe(4) cluster as a function of temperature using molecular dynamics. We report the interbasin isomerization rate and the bond fluctuation parameter obtained from these calculations. At 7 K, the isomerization rate is on the order of 0.01 ns(-1); at 20 K, the isomerization rate is greater than 10 ns(-1). Furthermore, at 7 K, the bond fluctuation parameter is less than 3%; at 20 K, it is in the range of 10-15% (depending on the sampling time used). Using this information, together with Monte Carlo quenching data, we assign the 15-20 K feature in the heat capacity to a solid-liquid phase change and the 7-K peak to a solid-solid phase change. We believe this is the smallest Lennard-Jones cluster system yet shown to exhibit solid-solid phase change behavior.     

Spin-crossover behavior in cyanide-bridged iron(II)-gold(I) bimetallic 2D Hofmann-like metal-organic frameworks

The synthesis and characterization of new two-dimensional (2D) cyanide-bridged iron(II)-gold(I) bimetallic coordination polymers formulated, {Fe(3-Xpy)2[Au(CN)2]2} (py = pyridine; X = F (1), Cl (2), Br (3), and I (4)) and the clathrate derivative {Fe(3-Ipy)2[Au(CN)2]2}.1/2(3-Ipy) (5), are reported. The iron(II) ion lies in pseudoctahedral [FeN6] sites defined by four [Au(CN)2](-) bridging ligands and two 3-Xpy ligands occupying the equatorial and axial positions, respectively. Although only compounds 2 and 4 can be considered strictly isostructurals, all of the components of this family are made up of parallel stacks of corrugated {Fe[Au(CN)2]2}n grids. The grids are formed by edge sharing of {Fe4[Au(CN)2]4} pseudosquare moieties. The stacks are constituted of double layers sustained by short aurophilic contacts ranging from 3.016(2) to 3.1580(8) A. The Au...Au distances between consecutive double layers are in the range of 5.9562(9)-8.790(2) A. Compound 5, considered a clathrate derivative of 4, includes one-half of a 3-Ipy molecule per iron(II) atom between the double layers. Compound 1 undergoes a half-spin transition with critical temperatures Tc downward arrow = 140 K and Tc upward arrow = 145 K. The corresponding thermodynamic parameters derived from differential scanning calorimetry (DSC) are Delta H = 9.8 +/- 0.4 kJ mol(-1) and Delta S = 68.2 +/- 3 J K mol(-1). This spin transition is accompanied by a crystallographic phase transition from the monoclinic P2(1)/c space group to the triclinic P1 space group. At high temperatures, where 1 is 100% high-spin, there is only one crystallographically independent iron(II) site. In contrast, the low temperature structural analysis shows the occurrence of two crystallographically independent iron(II) sites with equal population, one high-spin and the other low-spin. Furthermore, 1 undergoes a complete two-step spin transition at pressures as high as 0.26 GPa. Compounds 2- 4 are high-spin iron(II) complexes according to their magnetic and [FeN6] structural characteristics. Compound 5, characterized for having two different iron(II) sites, displays a two-step spin transition with critical temperatures of Tc(1) = 155 K, Tc(2) downward arrow = 97 K, and Tc(2) upward arrow = 110 K. This change of spin state takes place in both sites simultaneously. All of these results are compared and discussed in the context of other {Fe(L) x [M(I)(CN)2]} coordination polymers, particularly those belonging to the homologous compounds {Fe(3-Xpy)2[Ag(CN)2]2} and their corresponding clathrate derivatives.     

Structural Phase Transitions and Magnetic Superexchange in MIAgIIF3 Perovskites at High Pressure**

Pressure-induced phase transitions of M^IAg^IIF₃ perovskites (M=K, Rb, Cs) have been predicted theoretically for the first time for pressures up to 100 GPa. The sequence of phase transitions for M=K and Rb consists of a transition from orthorhombic to monoclinic and back to orthorhombic, associated with progressive bending of infinite chains of corner-sharing [AgF₆]⁴⁻ octahedra and their mutual approach through secondary Ag⋅⋅⋅F contacts. In stark contrast, only a single phase transition (tetragonal→triclinic) is predicted for CsAgF₃; this is associated with substantial deformation of the Jahn–Teller-distorted first coordination sphere of Ag^II and association of the infinite [AgF₆]⁴⁻ chains into a polymeric sublattice. The phase transitions markedly decrease the coupling strength of intra-chain antiferromagnetic superexchange in MAgF₃ hosts lattices.     

Helical polymer 1/infinity[P2Se6(2-)]: strong second harmonic generation response and phase-change properties of its K and Rb salts

The selenophosphates A2P2Se6 (A = K, Rb) crystallize in the chiral trigonal space group P3121, with a = 7.2728(9) A, c = 18.872(4) A, and Z = 3 at 298(2) K and a = 14.4916(7) A, c = 18.7999(17) A, and Z = 12 at 173(2) K for K+ salt and a = 7.2982(5) A, c = 19.0019(16) A, and Z = 3 at 100(2) K for Rb+ salt. The A2P2Se6 feature parallel one-dimensional helical chains of 1/infinity[P2Se62-] which depict an oxidative polymerization of the ethane-like [P2Se6]4- anion. On cooling well below room temperature K2P2Se6 exhibits a displacive phase transition to a crystallographic subgroup and forms a superstructure with a cell doubling along the a- and b-axes. The Rb analogue does not exhibit the phase transition. The compounds are air stable and show reversible glass-crystal phase-change behavior with a band gap red shift of 0.11 and 0.22 eV for K+ and Rb+ salts, respectively. Raman spectroscopy, 31P magic angle spinning solid-state NMR, and pair distribution function (PDF) analysis for crystalline and glassy K2P2Se6 give further understanding of the phase transition and the local structure of the amorphous state. K2P2Se6 exhibits excellent mid-IR transparency and a strong second harmonic generation (SHG) response. The SHG response is type-I phase-matchable and in the wavelength range of 1000-2000 nm was measured to be 50 times larger than that of the commercially used material AgGaSe2. Glassy K2P2Se6 also exhibits an SHG response without the application of electric field poling. In connection with the NLO properties the thermal expansion coefficients for K2P2Se6 are reported.     

Systeme Binaire AgNO3-LiNO3. Diagramme de phases et proprietes thermodynamiques des mélanges a l’etat liquide

To study the coherence of thermodynamic data of the AgNO₃-LiNO₃ -RbNO₃ ternary system, phase diagram of the binary system AgNO₃ -LiNO₃ has been obtained between 303 and 550 K by direct and differential thermal analysis technique. This system is characterized by an eutectic point (25% mol. LiNO₃ , 445±1 K) and a plateau due to the solid-solid transition in AgNO₃ at 434±1 K. In the solid state the solubility of each component in the other seems to be nil or negligible (no more than a few percents). Using other thermodynamic data, the excess properties of the binary liquid (AgNO₃ - LiNO₃ ) were calculated at 623 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Unprecedented association of [Mo6Br(i) 7Y(i)Br(a) 6]3- cluster units and [Mo(III)Br6]3- complexes: synthesis, crystal structures, and properties of the double salts Rb3[Mo6Br(i) 7Y(i)Br(a) 6](Rb3[MoBr6])3 (Y=Se, Te)

The double salts Rb(3)[Mo(6)Br(i) (7)Y(i)Br(a) (6)](Rb(3)[MoBr(6)])(3) (Y=Se, Te) result from the partial disproportionation of the Mo(6)Br(12) octahedral-cluster-based bromide, in the presence of corresponding chalcogenides and RbBr salt (crystal data: Rb(12)[MoBr(6)](3)[Mo(6)Br(i) (7)Te(i)Br(a) (6)] (1), Pm$\bar 3$m (No. 221), a=12.1558(2) A, Z=1, R(1)=0.028; wR(2)=0.050; Rb(12)[MoBr(6)](3)[Mo(6)Br(i) (7)Se(i)Br(a) (6)] (2), Pm$\bar 3$m, a=12.144(3) A, Z=1, R(1)=0.028; wR(2)=0.050). The structures of 1 and 2 are built up from [Mo(III)Br(6)](3-) complexes and [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) cluster units characterised by a random distribution of seven bromine and one chalcogen ligands on all the eight inner positions that face cap the Mo(6) clusters. Such a distribution implies a static orientational disorder of the [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) units around the origin of the unit cell. Close-packed anionic layers based on [Mo(III)Br(6)](3-) complexes and [Mo(6)Br(i) (7)Y(i)Br(a) (6)](3-) cluster units are stacked in the sequence ABC. This arrangement leads to very short Br(a)--Br(a) intercluster unit distances of 3.252 A, much lower than the sum of the van der Waals radii (3.70 A). The trivalent oxidation state of molybdenum in the Mo complexes and 24 valence electrons per Mo(6) cluster have been confirmed by magnetic susceptibility measurements. Salts 1 and 2 constitute the first examples of structurally characterised bromides containing discrete [Mo(III)Br(6)](3-) complexes obtained by means of solid-state synthesis.     

Synthesis,structure and spin-crossover transition of The Cluster Compound Nb6I11−xBrx (0 ⩽ x ⩽ 2.7)

The homogeneous phase Nb₆I_11?xBr_x (0 ? x ? 2.7) is synthesized from Nb₃Br₈, Nb₃I₈ and Nb in sealed Nb capsules at 1 130 K. A second-order phase transition is found as for the composition Nb₆I₁₁ itself, changing the space group from P2₁cn (low temperatures) to Pccn, accompanied by a spin-crossover from a doublet to a quartet state. With increasing Br content the lattice constants decrease and the transition temperature shifts from 274 to 170 K while the transition interval is broadened simultaneously. Single crystal investigations for x = 0.5 and 2.3, each at 110 and 298 K, indicate a preferred substitution of one of the bridging I positions (I6) by Br atoms.     

YbCl3-MCln体系相图的研究(M=Li、Mg、Ca、Pb; n=1,2)

借助于DTA与X射线衍射法研究了YbCl_3-MCl_n(M=Li、Mg、Ca、Pb; n=1或2)二元体系相图．发现YbCl_3-LiCl体系相图属固液异组成型，有化合物Li_3YbCl_6生成，它在481 ℃有一相转变. 其无变点分别为x_(YbCl_s)＝0.410；526 ℃和x_(YbCl_3)=0.340，547 ℃；YbCl_3-MgCl_2属类转熔型相图，在富YbCl_3相区666 ℃有一尚不知其性质的热效应，为x_(YbCl_3)＝0.380，628 ℃；YbCl_3-CaCl_2和YbCl_3-PbCl_2体系皆属简单低共熔型相图，其低共溶点分别为x_(YbCl_3)＝0.530, 615 ℃和x_(YbCl_3)＝0.340, 415 ℃. 后者在固相下有一不稳定化合物PbYbCl_5生成，在392 ℃分解，同时探讨了相图的某些规律．     

四氯合金属(II)酸烷铵在280-500K间的热力学性质和相变:III.四氯合镉(II)酸n-十二烷铵

在280-500K温度范围内用自动绝热量热计测量了(n-C~1~2H~2~5NH~3)~2CdCl~4的热容。在所研究的温度范围内发现一个固-固相转变, 其相变温度, 相变焓和相变熵分别为(332.4±0.1)K,(48.35±0.33)kJ.mol^-^1和(145.5±1.0)J.K^-^1.mol^-^1。结合已发表的(n-C~1~2H~2~5NH~3)~2MCl~4(M=Mn, Zn)的相变参数讨论了此类配合物的中心原子对其相变的影响。[MCl~4]^2^-配位方式的不同被认为是该类配合物的相变热参数产生差异的主要原因。     

Syntheses, structure, and bonding of Rb14(Mg1-xInx)30. A nonstoichiometric phase with an unusual substitution in the anion framework

The title compound Rb(14)(Mg(1-x)In(x))(30) (x = 0.79-0.88) has been obtained from high-temperature reactions of the elements in welded Ta tubes. There is no analogous binary compound without Mg. The crystal structure established by single-crystal X-ray diffraction means (space group P2m (No. 189), Z = 1 and a = b = 10.1593(3) Angstroms, c = 17.783(1) Angstroms for x = 0.851) features two distinct types of anionic layers: isolated pentacapped trigonal prismatic In(11)(7-) clusters and condensed [(Mg(x)In(1-x))(5)In(14)](7-) layers. The latter consists of analogous M(11) (M = Mg/In) fragments that share prismatic edges and are interbridged by trigonal M(3) units. The structure shows substantial differences from related A(15)Tl(27) (A = Rb, Cs) in which the cation A that centers a six-membered ring of Tl(11) fragments is replaced by M(3.) Both linear muffin-tin orbital and extended Hückel calculations are used to analyze the observed phase width and site preferences. We further utilize the results to rationalize the distortion of the M(11) fragment in the condensed layer and also to correlate with electrical properties. An isomorphous phase region (Rb(y)K(1-)(y))(14)(Mg(1-x)In(x))(30) (y = 0.52, 0.66 for x = 0.79) is also formed.     

Phase Transitions in Three New Hybrid Crystals: (Me3NR)4[Ni(NCS)6] (R=Ethyl,Propyl, and Butyl)

Understanding the microscopic origin of phase transitions in hybrid crystals is of significant important but challenging for designing novel phase-transition materials. Here, three new hybrid crystals, (Me₃NR)₄[Ni(NCS)₆] (R=ethyl for 1 , propyl for 2 , and butyl for 3 ) were synthesized and comprehensively studied on their crystal structures, intermolecular interactions, and phase transitions. They possess a same anti-XeF₄ structure mode but exhibit different phase transitions arising from their subtly changed alkyl groups. Specifically, 1 undergoes four-step P2₁/c-P2₁/c-P2₁/c-Pbca-Cmce crystalline transitions at 165, 203, 244, and 280 K, respectively; 2 undergoes three-step P2₁2₁2₁-Pbca-P2₁/n-P 1c crystalline transitions at 167, 393, and 410 K, respectively, following by a solid-liquid transition at 453 K; 3 undergoes an iso-space-group P2₁/n-P2₁/n crystalline phase transition at 257 K and a solid-liquid transition at 410 K. These instances well demonstrate the key roles of delicate and complicated intermolecular interactions on inducing nontrivial phase transitions in hybrid crystals.