Alain Meresse

Raman scattering and X-ray diffraction study of structural phase transitions in the perovskite-type layer compound (C3H7NH3)2CdCl4

Abstract The structural phase transitions of (C3H7NH3)2CdCl4 (PACC) have been studied by means of Raman scattering. X-ray diffraction and DSC measurements It is shown that the order-disorder phase transition Abma ↔ Pbca occurs at 156 K and not at 183 K as previously proposed by Chapuis (Acta Cryst B34, 1506 (1978)) Apparently, the transition at 183 K does not change the Abma space group; it is suggested that it could be related to the occurrence of an incommensurate phase Another structural transformation of PACC is detected at 114 K, but no conclusion can be given as far as the structure of the low-temperature phase is not determined.

Polymorphism in the Bidimensional compound (n-C16H33NH3)2CdCl4

Abstract Four crystalline phases have been observed in the perovskite-type layer compound ( n -C 16 H 33 NH 3 ) 2 CdCl 4 using X-ray diffraction, differential scanning calorimetry and vibrational analysis. Phase IV, stable at low temperature, has a monoclinic ordered structure. The two intermediate phases III and II are orthorhombic and the high temperature form I is tetragonal. In the last case, the diffraction pattern shows the presence of a diffuse scattering phenomenon corresponding to the bidimensional melting of only the organic part of the structure (C 16 H 33 NH 3 chains). Entropy values of the order-disorder process are best interpreted by a disorder similar to that of the molten state of the n -paraffins. The largest enthalpies are measured at the (IV-III) and (II-I) transitions; they correspond to the two discontinuities of the interlayer spacing and are related to a modification of the organic chain length due to the occurrence of kink defects ( GT 2 n +1 G ′), and a decrease of the number of trans forms between the G and G ′ bonds, respectively.

Electromagnetic immunity model of an ADC for microcontroller’s reliability improvement

This paper deals with the study of electromagnetic compatibility prediction of integrated circuits in order to improve their reliability. The study takes place in the context of embedded electronic circuit where the proximity of the analog and digital parts increases. The case of microcontroller is considered and more particularly the susceptibility of the Analog to Digital Converter (ADC) device. The use of the new immunity approach (ICIM-CI model) is proposed to achieve the susceptibility modelling of the ADC. The model is built step by step (functional and coupling path models). Then, it is possible to estimate the effect of disturbances on the sensitive nodes. Finally the aim of EMC circuit compliance is enhanced.

Structure of Di-Tetramethyltetraselen-afulvalenium Perchlorate (TMTSF)2 CϱO4 in its Low Temperature (T ∼ 10 K) Ordered Phase

Abstract At T ∼ 24K, the quasi one dimensional organic superconductor (TMTSF)2CϱO4 shows a structural transition leading to a doubling (a × 2b × c) of the unit cell. The neutron average structure (i.e. superlattice reflections not included) at T = 7K has already been published. In the present paper, we report the results of a rigid body refinement of the low temperature (T ∼ 10K) structure from both the earlier set of neutron main reflection intensities and an extra set of X-ray superlattice intensities. This improved structural description clearly shows that the anion orientations alternate in the b direction only and that there is no significant TMTSF displacement from the average position. We compare these results with recent structural data obtained on (TMTSF)2ReO4 which exhibits below T ∼ 180 K an insulating ground state instead of the metallic one for the perchlorate salt.

A Characteristic Order-Disorder Molecular Phase Transition in 2-Chloronaphthalene

Abstract An order-disorder phase transition has been studied in 2-Chloronaphthalene by both calorimetry and X-Ray diffraction. The transformation is reversible and does not destroy the single crystal. It extends over a large temperature range 253-309 K and can be considered as a “high order” transition: the high temperature form corresponds to a totally disordered phase and the low temperature form to a semi-ordered one.

Low Temperature (4K) and High Pressure (6.5 Kbars) Crystal Structures of (TMTSF)2PF6

Abstract We have performed structural investigation of the (TMTSF)2PF6 salt at low temperature (neutron diffraction) and under pressure (X. Ray diffraction). Evolutions of the main structural parameters are described. Their descriptions allow the first structural approach of pressure effects on the Bech-gaard salts and give comparative informations for a same compound.

Transitions de phase destructive et non destructive dans le cristal moleculaire bromo-2 naphtalene

Abstract The polymorphism of 2-bromonaphthalene has been studied by both crystallographic and energetical methods. Three crystalline forms have been characterized, respectively denoted Br III , Br II and Br I . The first one is the stable form up to 319 K. At this temperature a first order phase transition occurs which breaks the single crystal and leads to a disordered structure Br I isotypic with the naphthalene one. The Br II form is a metastable one which appears when cooling the Br I , form; when so formed, the Br II phase can give again the Br I one by annealing; so that the Br I -Br II transition is reversible. This second order transition extends over a large temperature range (275–319 K), it does not destroy the single crystal and corresponds to a substructural modification along the c axis of the monoclinic cell. The anomalies of the Cp curve and the variations of the principal components of the thermal expansion tensor suggest that there are two competitive temperature dependent molecular reorientations. The transition Br II →Br III which leads to the stable ordered form is spontaneous at room temperature, it takes place sluggishly and destroys the single crystal. Cell parameters of the Br III form have been determined from powder data using an automatic indexing method: a = 9.578(1) A, B = 9.601(1) A, c = 10.303(1) A, α = 100.79(1)°, β = 109.06(1)°, γ = 101.77(1)°. (Figure of merit M 20 = 86.)

Thermal expansion of the disordered form of 2-fluoronaphthalene (form I)

The thermal-expansion tensor of the disordered form of 2-fluoronaphthalene (C10H 7F) was calculated from the changes of the lattice constants with temperature (273–323 K) as measured with X-ray and neutron diffraction. The results show that the thermal-expansion anisotropy is significant. The structural interpretation of this property is not trivial.

Structural phase transitions in tmmc and tmcc

Abstract The structural phase transitions occurring in TMMC and TMCC are studied by means of DSC, X-ray diffraction and diffuse scattering, Raman scattering and ultrasonic measurements. A phenomenological model based on Landau theory is proposed.

Etablissement du diagramme binaire hydroxy.2 naphtalene-chloro.2 naphtalene par differentes analyses thermiques

The phase diagram of the 2-chloronaphthalene-2-hydroxynaphthalene binary system has been established in three thermal investigations (calorimetric, crystallographic and optical methods). This diagram is fairly complicated. The main feature is the presence of three invariants: a eutectoid atTe=309 K, a peritectic atTp=333 K and a metatectic atTm=364 K.ZusammenfassungDas Phasendiagramm des binären Systems 2-Chlornaphthalen-2-Hydroxynaphthalen wurde fürT⩾293 K mittels drei thermischer Analysenmethoden (kalorimetrische, kristallographische und optische Methoden) aufgestellt. Das Diagramm ist verhältnismäßig kompliziert. Der wichtigste Wesenszug ist das Vorliegen von drei Invarianten: einer eutektoidischen beiTe=309 K, einer peritektischen beiTp=333 K und einer metatektischen beiTm=364 K.РезюмеКалориметрическим, к ристаллографически м и оптическим методами изучена фазовая диаграмма дв ойной системы 2-хлорнафталин-2-оксина фталин при температу реT ⩾ 293 K. Диаграмма являетс я относительно сложн ой и для которой характерным является наличие тре х инвариантных систе м: эвтектики приT3=309 K, перитектики пр иTn=333 K и метатектики приTM=364 K.