Etude de la conductivite ionique dans le tantalate de lithium LiTa3O8β

The study of the electrical properties of LiTa₃O₈β by the complex impedance method characterizes a conductivity due to moving of the lithium ions inside the tunnels of the lattice.     

Repartition cationique et structure magnetique de Cs2MnNiF6

A neutron diffraction study of Cs₂MnNiF₆ shows that the cationic distribution differs from that of the apparently isostructural 12R - Cs₂NaCrF₆ (R3̄m). Below the ordering point the magnetic cell is identical with the crystallographic one and the moments are perpendicular to the c axis. Ferromagnetic couplings inside MnNi₂F₁₂ units (three face-shared octahedra) and antiferromagnetic interactions between these units and corner-shared MnF₆ octahedra are observed.     

Synthese et caracterisation de verres fluores dans le systeme BaF2-UF4-FeF3-MnF2

The investigation of the quaternary system BaF₂-UF₄-FeF₃-MnF₂ shows up large vitreous areas in the four ternary systems. The existence of a large unique vitreous area inside the quaternary system confirms the particular behavior of Mn²⁺ ion among 3d transition ions and is in agreement with the compact fluorine stacking view of fluoride glasses.     

Structure et conductivite electrique de verres appartenant au systeme Li2Si2O5 Li2SO4

The conductivity of vitreous electrolytes belonging to the Li₂Si₂O₅ Li₂SO₄ system has been measured over the temperature range 25–300 °C and for Li₂SO₄ concentrations varying from 0–28 mole percent. It has been found that the conductivity increases with the Li₂SO₄ fraction, attaining 10^?5 Ω^?1 cm^?1 at 130°C for the glass containing the highest proportion of sulphate. Raman spectroscopic studies indicate that the tetrahedral SO^2?₄ ions are in the glassy network, inserted or not into the silicate chains.     

Phases de type alumine β et β″ dans le systeme Na2O  Ga2O3

The study of a Na₂O  Ga₂O₃ system - the contents in Ga₂O₃ being superior to 75 moles % - determines precisely the field of existence of the phase of the β alumina type and it gives evidence of another phase of a β″ alumina type which is close to the composition 5,33 Ga₂O₃  Na₂O.The investigation, through X-rays, of single crystals of the two phases β and β″ makes certain the hexagonal and rhomboedral symetries of the β and β″ alumina type. The β phase presents a high ionic conductivity similar to that of the β alumina.     

Groupe spatial et ordre des atomes de zinc et de germanium dans ZnGeN2

By means of neutron diffraction it has been possible to observe ordering of Zn and Ge atoms in the normal tetrahedral compound ZnGeN₂. The structure is thus of FeNaO₂ type, with space group Pna2₁.     

Cinétique de croissance de Ge/Ge et Ge/GaAs dans le système Ge---H2---He---I2

Des couches monocristallines de germanium ont été obtenues sur des substrats de germanium et GaAs par transport chimique mettant en jeu une réaction de disproportionnation avec H₂, hélium et I₂. Les vitesses de croissance sont des fonctions de la température de substrat, de la pression initiale d'iode et de la fraction molaire F de H₂ dans le mélange H₂---He.

Afin de définir les conditions de transport par l'iode, les équilibres obtenus quand le germanium est mis en présence de I₂, H₂ et hélium sont étudiés. Deux régions peu sensibles à la température ont été mises en évidence: elles correspondent aux températures de source et de substrat. La concentration en porteurs et la mobilité de Hall de couches Ge/GaAs et Ge/Ge sont présentées.     

Mise en evidence de tetraedres PN4 dans le nitrure Mg2PN3 de type wurtzite

Mg₂PN₃ has been prepared by reaction in solid state between Mg₃N₂ and P₃N₅. It crystallizes with orthorhombic symmetry, space group Pna2₁, with unit cell parameters a = 9.759 (5), b = 5.635 (3), $\text{c}\text{= 4.743 (3)}\text{A}\text{?}\text{z}\text{= 4}$. Its structure is related to the wurtzite type with Mg and P atoms ordered. It is the first example of PN₄ tetrahedra in a normal tetrahedral structure.     

Etude des solutions solides entre le sesquioxyde de fer cubique γ-Fe2O3 et le ferrite de zinc ZnFe2O4

The authors have prepared metastable solid solutions between cubic iron sesquioxide γ-Fe₂O₃ and zinc ferrite ZnFe₂O₄. They give the main characteristics of these defect spinels. Fe³⁺ ions and vacancies are replaced by Zn²⁺ ions on tetrahedral sites. The lattice parameter and the thermal stability increase with the substitution rate. The magnetic behavior is comparable to that observed for solid solutions M_1?yZn_yFe₂O₄.     

Synthese,etude cristallochimique et conductivite ionique de quelques aluminosilicates de lithium de type spodument β (LiAlSi2O6)

Solid solutions Li_1+xAl_1+xSi_2?xO₆, Li_1?xAl_1?xSi_2+xO₆, Li_1?xAlSi_2?xM_xO₆ (M = P, V) all of the β-spodumene type, have been synthesised and the limits of their homogeneity ranges established. The ionic conductivity of sintered ceramics has been measured between 200 and 600°C by the complex impedance method. Its observed evolution (increase and then decrease with increasing substitution rates) is discussed in terms of a compensation mechanism between the relative evolution of the numbers of respectively charge carriers and empty sites. Influence of sintering process on conductivity has been shown by comparison of naturally sintered, hot-pressed and glassy samples.     

Synthese et etude de verres fluores dans les systemes LnF3BaF2MnF2

New heavy metal fluoride glasses based on MnF₂ and rare-earth fluorides LnF₃ are reported. Vitreous materials have been obtained by quenching for Ln = Dy → Lu + Y; the limits of the glassy domain and the typical temperatures Tg, Tc, Tf are given. Optical measurements indicate that the I.R. absorption edge is situated in the 9–10 μm region.     

La conductivite ionique dans CaF2−xHx

NMR experiments performed on ¹H and ¹⁹F in CaF_1.06H_0.94 between 296 and 430 K show a motional narrowing of the proton line for T > 365 K and a rigid lattice behaviour of the fluorine line. Thus, it appears that the ionic conductivity of this material is due to the mobility of H^? ions, with an activation energy of 0.45 ± 0.05 eV.     

Électroluminescence de couches minces de CdF2: Mn et CdF2: LnF3

The electroluminescence of thin films of CdF₂ was observed using an MISM structure (CdF₂:Mn, CdF₂:LnF₃). The use of the Eu³⁺ ion as an optical structural probe suggests O_h and C_nv symmetries for the Ln³⁺ site. The addition of Na⁺ induces a long range charge compensation following which only the O_h point symmetry is observed.     

Synthese et etude de la conductivite anionique des phases du systeme NaF - BiF3

A definite NaBiF₄ phase and a solid solution Na_1?xBi_xF_1+2x (0,60 ? x ? 0,70) of fluorite derived type have been obtained at 430°C in the NaF - BiF₃ system. Investigation of the electrical properties of these materials shows that Na_0,40 Bi_0,60 F_2,20 is the best anionic conductor of the system, with a conductivity of about 10^?3 Ω^?1 cm^?1 and 100°C and an activation energy of 0,46 e v. The results are discussed in comparison with those previously obtained for the KF - BiF₃ and RbF - BiF₃ systems.     

Classement des porteurs de charge et conductivite du compose K8Na4Sb12O36 de structure KSbO3 cubique

Two structures have been reported for cubic KSbO₃ type. One has space group Pn3, where K⁺ ions are in an ordered state. The other has Im3 with K⁺ ions in a disordered state. These ions are weakly bound in large tunnels along 〈111〉 and are mobile along them three-dimensionally.The presence of two alkaline cations in these tunnels is in favour of the ordered state. Single-crystals of K₈Na₄Sb₁₂O₃₆ are obtained and crystallize in the space group Pn3, $\text{a}\text{= 9,515(3)}\text{A}\text{?}$. Using 563 independent reflections, the structure has been refined by full-matrix least squares, to factor R = 0,059.The comparison of the ionic conductivity of ordered (Pn3) and disordered (Im3) compounds is studied by the authors.     

Elaboration et caracterisation de monocristaux de V2O3 par transport en phase vapeur

Single crystals of V₂O₃ are obtained by HCl or TeCl₄ chemical transport method in sealed quartz tubes with temperature gradients of 1050–930°C and 990–900°C respectively. The hexagonal prims are 5 mm long and 1 or 2 mm wide. Both kinds of crystals are characterized by sharp insulator-metal transition at 156 and 137 K respectively, they present a large hysteresis. The sharp decrease in resistivity with increasing temperature is of the order of 10⁸ at the transition.     

Verres mixtes LiPO3ZnCl2 et LiPO3AlCl3 conductivite electrique; approche structurale

Following our attemps of comparisons between the glasses containing AgPO₃ and the glasses containing LiPO₃, data on the glass transition temperatures, the electrical conductivities and Raman spectra of the LiPO₃ZnCl₂ and LiPO₃AlCl₃ glasses are reported. A mechanism of exchange of ions has been already proposed to explain the properties of the AgPO₃MI₂ (with M = Pb, Cd, Sr, Hg) and AgPO₃MI (with M = Na, K) glasses. Such an hypothesis does not agree with the properties of the LiPO₃ZnCl₂ glasses but seems to be still valid for the LiPO₃AlCl₃ glasses.     

Synthese et conductivite des verres du systeme B2O3Na2ONa2SO4

New glasses with sodium ion carriers have been obtained in the B₂O₃Na₂ONa₂SO₄ system. Their conductivities have been measured vs temperature and composition. Raman spectroscopy brings information about the behavior of sodium sulfate in the vitreous matrix.     

Proprietes electriques et magnetiques de Mn0,25NbS2 et Mn0,33NbS2

Crystals of Mn_0.25NbS₂ and Mn_0.33NbS₂ phases were grown by iodine vapor transport. Their accurate composition has been determined and single phase specimens used for studies of magnetic and electrical properties. Both compounds show ferromagnetic interactions at low temperature. Curie paramagnetic temperatures are 120°K for Mn_0.25NbS₂ and 53°K for Mn_0.33NbS₂. The experimental magnetic moments indicate an intermediate valence state (between +2 and +3) for manganese in the compounds. Resistivity and Hall measurements show a metallic character and coincide with the intermediate valence state. Interpretations are given in terms of a simple band model, and an analysis of the magnetic interactions is proposed.