S. Vilminot

Etude des proprietes structurales et electrioues d'un nouveau conducteur anionique: PbSnF4

Three allotropic varieties of PbSnF4 - α, β and γ - have been detected by DTA and X-ray diffraction. The α ai β and β ai γ transitions are reversible and occur at 80 and 355°C respectively. The high temperature form γ - PbSnF4 is cubic and of fluorite type. The structures of the tetragonal β - PbSnF4 and the orthorhombic α - PbSnF4 forms are derived from the same structural type. PbSnF4 has a high anionic conductivity (σ200°C ⋍ 10−1 Ω−1cm−1). The temperature dependence of the conductivity indicates the existence of a break in the activation energy at 90°C.

About the allotropic transformations of PbSnF4

Abstract Microcalorimetric and dilatometric studies of PbSnF 4 give evidence of several allotropic forms for PbSnF 4 . The complex thermal behaviour may be summarized as follows : . The crystallographic data of the detected allotropic forms have been determined by investigations on single crystals. All structures derive from the fluorite-type. The obtained results confirm a previous work of the authors, new more precise techniques bringing further information.

Characteristics of an oxygen gauge at temperatures lower than 200°C

Oxygen gauges involving a PbSnF4 electrolyte were tested at temperatures lower than 200°C. The Sn-SnF2 mixture was used as a reference electrode. Various electrode materials were investigated (metals, oxides with perovskite or rutile structures). The selected electrode material was RuO2. Doping of the fluoride electrolyte with peroxide ions improves noticeably the performances of the gauge (stability of the response, time-lag, etc.). In the temperature range 150–200°C, the response time of the gauge is of the order of one minute in the oxygen pressure range 10−3 - 1 atm.

High ionic conductivity in new fluorine compounds of tin II. I. On PbSnF4: Relation between structure and conductivity

Abstract The structural determination of the monoclinic form of PbSnF 4 shows a cationic network as in the fluorite structure. The high value of the F − mobility seems to be correlated to a great number of vacancies in the anionic network.

NMR and electrical conduction study of fluorine motion in MSn2F5 compounds with M=Na, K, Rb, Cs, Tl, NH4

Abstract The fluorine motion in MSn2F5 compounds was investigated using NMR measurements of spin lattice relaxation times T1 at various temperatures and frequencies. In the 250 K – 420 K temperature range the T1 behaviour is quite similar for MK, Rb, T l , NH4. Activation energies and correlation times are deduced from these data. NMR and conductivity results show that fluorine ion exhibit a high mobility. Taking into account crystallographic data it is shown that electrical conductivity is strongly dependent on the cation polarisability and is due to the motion of fluorine ions inside SnF layers on partially occupied sites.

High ionic conductivity in new fluorine compounds of tin II. II. On the binary system PbF2-SnF2

Abstract The PbxSn1−xF2 solid solutions adopt various structural types following the x value. We observed an evolution from a completely disordered structure for the phases with high lead concentration to an ordered structure for x=0.5. The increase of the logarithm of the conductivity with x is explained by the increase of the number of vacancies in normal anionic positions when the ratio of Sn 2+ Pb 2+ is increasing.

Sur une serie d'oxyfluores du chrome VI de formule MCrO3F où M = K, Rb, Cs et NH4

Abstract The compounds MCrO 3 F, (M = K, Rb, Cs and NH 4 ) have been prepared, then studied by X-Ray. diffraction — From these results it appears a different occupation of the same crystallographic position by O and F at the top of the tetrahedron CrO 3 F − against M. That means a different reactivity of these compounds and shows the importance of the F atom. The distances CrO(1,60A) and CrF (near of 1,74 A) are discussed. The CrO 3 F − compounds are compared with SO 3 F − , ClO 4 − , CrO 3 Cl − and PO 2 F 2 − compounds.

Etude du comportement thermique de PbSnF4 par analyse calorimetrique differentielle

Abstract The thermal behaviour of PbSnF 4 has been studied by means of a differential scanning calorimeter over the range 298–700 K. Five allotropic forms of PbSnF 4 have been found and the associated enthalpies of transition have been measured. The crystallographic data have been determined for the allotropes by single cristal studies.

Les proprietes de transport d'halogenures d'etain divalent

Abstract The ionic conductivity of SnF 2 and SnFCl has been studied by the complex impedance method: SnF 2 has electric properties close to those of the fluorine-type β - PbF 2 . The fluorine mobility in SnFCl is low in comparison with α - PbF 2 despite similar structures. These features are explained on the base of structural and size considerations.