R. Mercier

Microstructure modification of amorphous titanium oxide thin films during annealing treatment

Abstract Thin films of titanium oxide have been deposited on (100) silicon wafers and on quartz substrates by reactive r.f. magnetron sputtering from a 99.6% pure Titanium target. Amorphous and overoxidised coatings (TiO2.2) have been obtained from this technique. The influence of the post-deposition annealing between 300 °C and 1100 °C on the structural and optical properties and on the surface morphology has been investigated. The results of X-ray diffraction showed that films annealed from 300 to 500 °C have an anatase crystalline structure whereas those annealed at 1100 °C have a rutile crystalline structure. Optical analyses showed that UV-Vis transmission spectra are strongly modified by the annealing temperature and refractive index of TiOx layers also changes. Atomic force microscopy measurements corroborate optical and structural analyses and showed that the surface of the coatings can have various appearances and morphologies for the annealing temperatures investigated.

Superionic conduction in Li2S - P2S5 - LiI - glasses

Abstract Studies on glass formation, structure and electrical condutivity have been carried out in the Li 2 S-P 2 S 5 -LiI system with the ratio Li 2 S/P 2 S 5 = 2. The addition of LiI lowers the glass transition temperature but does not break the P 2 S −4 7 units. At 25°C the conductivity is the higher one, about 10 −3 (Ω cm) −1 at the boundary of the glassy region (x=0, 45) with a corresponding E c value of ≅7kcal.mole −1 in the temperature range between −30°C and Tg. The conduction is essentially ionic in nature and due the lithium ions.

Ionic conductivity of and phase transition in lithium thiophosphate Li3PS4

Abstract A phase transition of Li 3 PS 4 has been revealed at 190°C both by DTA and by a discontinuity in the Arrhenius plots of conductivity. The conductivity is increased by a step of 0.5 (log σ), and the low and high temperature ranges are characterized by activation energies of respectively 0.49 (±0.01) eV and 0.46 (±0.01) eV. A small order-disorder of the Li + ion distribution might be the source of this phenomenon; Li 3 PS 4 may be considered as a good lithium crystalline electrolyte ( σ 25°C =3 × 10 −7 S cm −1 ).

Vibrational properties of and short range order in superionic glasses AgPO3−AgX (X = I, Br, Cl)

Abstract Raman scattering measurements are reported for different glasses containing silver halides. The high frequency (Δ v > 250 cm -1 ) study implies that the interactions between the phosphate network and the halide solutes are very weak. Area measurements of the two low-frequency bands ( -1 ) have shown that: (i) the very low frequency band (∼60 cm -1 ) is only correlated to all Ag + oscillations; (ii) the higher band shifts from 115 cm -1 (AgI) to 135 cm -1 (AgBr) and to 190 cm -1 (AgCl) and its integrated intensity is in linear relation to the AgX concentration. The mode has been assigned to symmetric vibrations involving both Ag + and X - ions line in αAgI. A local cluster model of tetrahedral (AgX) n species has been proposed for each glass.

Structure determination of AgPO3 and (AgPO3)0.5(AgI)0.5 glasses by neutron diffraction and small angle neutron scattering

Abstract Neutron diffraction and small angle neutron scattering (SANS) were performed on AgPO 3 and (AgPO 3 ) 0.5 (AgI) 0.5 glasses. AgPO 3 glass is made up of long chains of PO 4 tetrahedra joined together by Ag atoms. When silver iodide is added, the radial distribution function shows a large peak at 2.83 A, due to AgI interactions. AgI does not modify the network forming unit. The existence of small clusters is confirmed by analysing the coordination number of AgI pairs obtained by subtracting the experimental structure function of the AgPO 3 glass from that of the corresponding AgI-doped glasses. A rough estimation of their size is given by SANS experiments. Not all the AgI pairs are involved in AgI cluster units. The compatibility of the results obtained with recent structural investigations by non diffractometric techniques is examined.

Quasielastic and inelastic neutron scattering from AgPO3−AgI glass

A quasielastic neutron scattering experiment was performed on the fast ionic conductor AgPO3-Agl, which is a vitreous electrolyte. This experiment was performed on the time-of-flight spectrometer IN 6 of the Institut Laue-Langevin in Grenoble, with the following parameters: λ=5.1 A; 1.25 A;-1<Q<2.04-1; instrumental resolution— FWHM=0.070 meV; sample thickness: 1.5 mm, 299 K <T< 368 K. The spectra generally show a quasielastic broadening of the elastic peak and a long tail up to 10 meV which is due to an inelastic distribution. In order to obtain the quasi-elastic contribution, the profile of the central peak was fitted within ± 0.6 meV for nine different spectra and for five temperatures. The elastic incoherent structure factor (EISF) was constant at 85%. The profile of the quasielastic contribution was found to be Lorentzian. When plotting the energy width ΔE times S(Q), the coherent structure factor, versus Q2, a straight line is obtained for all temperatures. This means that the mechanism of the conductivity is certainly a translational diffusion with a coefficient of self-diffusion of the silver ions D=1.32x10-5exp(-2080⧸RT) (activation energy being in calories). The value of the activation energy is very close to that of α-AgI measured by electric conductivity. The value of EISF: 0.85 indicates that the observed quasielastic scattering is due to half of the silver ions. These two results seem to confirm our hypothesis on the structure of these glasses: small “clusters” of AgI with tetrahedral coordination are dispersed in the AgPO3 host glass. The two peaks observed in the inelastic frequency distribution function can be related to vibrations of the AgPO3 host glass and of AgI4 structural units respectively.

Correlation between structural and electrical properties in (1-x)AgPO3•xMX2 glasses (M=Pb2+, Hg2+; X=I−, Br−, Cl−) from Raman spectroscopy and ionic conductivity measurements

Abstract The ionic conductivity of (1-x) AgPO3·xMX2 (M = Pb, Hg and X = I, Br, Cl) was measured as a function of temperature from 25°C to Tg. The influence of the nature of the divalent cation is of primary importance. The conductivity of the Pb glass increases with x in the vitreous domain while the conductivityof the Hg glass increases with x until x=0.2 then becomes nearly constant. The conductivity of 0.81 AgPO3-0.19 PbI2 is close to that of 0.5 AgPO3-0.5 AgI while that of 0.5 AgPO3-0.5 HgI2 is much lower (∼103). Raman scattering spectra were recorded from 5 to 350 cm-1. No modifications of the (PO3)∞ chain skeleton occur when adding PbX2 or HgX2. On the other hand, AgX characteristic bands appear for the Pb glasses, while HgX2 molecular unit bands appear for the Hg glasses (when x>0.2). Explanations of such behaviour are given in terms of creation or non-creation of “AgX clusters” of “AgX, HgX2 clusters” in the AgPO3 host glass, by exchanging M2+ by Ag+ around the halide anions.

Study of Ca2+-induced silica coagulation by small angle scattering

Abstract The intefacial behavior of monodisperse (radius ≌ 15 nm) silica sols has been characterized by the evolution of their surface charge as a function of pH and salt concentration. The Ca2+ coagulation critical concentration, ccc, has been determined by turbidity between pH 7.5 and 9. The pH dependence of the calcium ccc shows that one adsorbed Ca2+ releases one H+ from the surface. Small angle neutron scattering gives a power law profile over one decade of Q for the silica aggregates. Their fractal dimension ranges from 1.7 to 2.1 depending on pH and [Ca2+; the faster the coagulation the greater the compacity. Small angle X-ray scattering (1.7 × 10−2

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd, Hg, Pb. Correlation entre conductivite et structure

Abstract The glass-forming regions in the AgPO 3 − MI 2 systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of 10 −2 (Ω cm ) −1 at 25°C is obtained for a mole fraction of 0,19 in PbI 2 or in CdI 2 , whereas a value of 3×10 −5 (Ω cm ) −1 at 25°C is found for a mole fraction of 0,5 in HgI 2 . The conductivity results and Raman spectra are examined and compared with those of AgPO 3 − AgI. An exchange between Ag + and M 2+ ions is proposed leading to AgI species in AgPO 3 − CdI 2 and AgPO 3 − PbI 2 glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.

Characterization of intermediate-range order in superionic AgPO3-AgX (X=I, Br, Cl) glasses by neutron diffraction

Abstract AgPO 3 -AgX glasses present a prepeak in the 0.5-0.9 A −1 Q -range. Using isotopic substitution in 0.75 AgPO 3 -0. AgCl ( 35 Cl , 37 Cl, natural Cl and 35 Cl - 37 Cl ) provokes a dramatic variation in the prepeak intensity, which is strong with 37 Cl and disa for 35 Cl. The intensity of the prepeak is well correlated to the contrast term ( ϱ AgPO 3 - ϱ AgX ) 2 corresponding to the square of the relative neutron scattering length densities. As in colloidal systems, this peak can be associated with an intermediate structure of particles lying inside a continuous host. The interparticle distance (comprised between 8 and 10 A) may be analysed in two models (i) “AgX” microdomains repeated in AgPO 3 matrix or (ii) “(PO 3 ) ∞ ” chain microdomains repeating inside a connective tissue made essentially of disordered AgI. The latter model could be more appropriate to describe other physical properties such as ionic conductivity.