Showing papers by "Josep Salud published in 2004"

Thermodynamic, crystallographic, and dielectric study of the nature of glass transitions in cyclo-octanol.

Abstract: –OH) is revealed to be a complexproblem and only two stable solid phases, denoted on cooling from the liquid as phases I and II, are foundusing static ~thermodynamic and x-ray diffraction! as well as dynamic ~dielectric spectroscopy! experimentaltechniques. Both solid phases are known to exhibit glass transitions if they are cooled down fast enough toprevent transition to ordered crystalline states. Although glass transitions corresponding to both phases hadbeen well documented by means of specific heat measurements, x-ray measurements constitute, as far as weknow, the first evidence from the structural point of view. In addition, a great amount of dielectric worksdevoted to phase I and its glass transition, were published in the past but next to nothing relating to thedielectric properties of phase II and its glass transition. The nature of the disorder of phase II will be discussed.DOI: 10.1103/PhysRevB.69.224202 PACS number~s!: 61.43.2j, 64.70.Pf, 65.60.1a, 77.22.2dI. INTRODUCTION

The Two-Component System CCl4 + CBrCl3. Inference of the Lattice Symmetry of Phase II of CBrCl3

Abstract: The phase diagram of the two-component system between two halomethanes, carbon tetrachloride (CCl4) and bromotrichloromethane (CBrCl3) has been determined by means of X-ray powder diffraction and thermal analysis techniques from 200 K to the liquid state. From the continuous series of mixed crystals, three relations of isomorphism have been evidenced: (i) between the stable low-temperature monoclinic (M) phases, (ii) between the stable orientationally disordered (OD) rhombohedral (R) phases, and (iii) between the stable OD face-centered cubic (FCC) of CBrCl3 and the metastable FCC phase of CCl4. The existence of such a metastable phase gives rise to the appearance, for a large range of composition, of metastable FCC mixed crystals that behave monotropically with respect to the R mixed crystals accordingly with the well-known monotropic character of the R to FCC phase transition of the CCl4. The isomorphism relationships i and ii enable us to validate the previously proposed structure of the monoclinic ph...

Multiple melting of orientationally disordered mixed crystals of the two-component system (CH3)2CCl2–(CH3)CCl3

Abstract: Orientationally disordered (OD) stable and metastable mixed crystals of the two-component system 2,2-dichloropropane ((CH3)2CCl2)+methylchloroform ((CH3)CCl3) have been characterized from crystallographic and thermodynamic points of view. Continuous series of mixed crystals in the stable rhombohedral (R) phase points out an isomorphism relationship. The monotropic behavior of the non-isomorphous OD metastable phases in the pure components (simple cubic, SC, and face-centered cubic, FCC, respectively) with respect to the R stable phase is partially retained by the mixed crystals. In particular, SC mixed crystals were found persistent enough as metastable crystals in the whole composition range with the exception of the pure compound (CH3)CCl3, for which only the FCC metastable phase was experimentally available. On the contrary, samples with compositions greater than X=0.70 in (CH3)CCl3 crystallized into either the FCC or SC, both being metastable with respect to the R phase. Thus, three kinds of OD mixed crystals appear which give rise to three independent OD+Liquid equilibria. The thermodynamic analysis of such non-interfering equilibria, [R+L], [SC+L] and [FCC+L], enables us to infer the stability relationships between the whole of OD phases.