Disordered LiZnVO4 with a phenacite structure

Single crystals of lithium zinc vanadate, LiZnVO4, were grown by the flux method. The structural type of this vanadate is characterized by a three-dimensional arrangement of tetra­hedra sharing apices in an LiZnVO4 network. This arrangement contains three different tetra­hedra, namely one [VO4] and two disordered mixed-site [Li/ZnO4] tetra­hedra. The resulting lattice gives rise to hexa­gonal channels running along the [0001] direction. Both sites in the mixed-site [Li/ZnO4] tetra­hedra are occupied by a statistical mixture of lithium and zinc with a 1:1 ratio. Therefore, LiZnVO4 appears to be the first vanadate known to crystallize with a disordered phenacite structure. Moreover, the resulting values of calculated bond valences (Li = 1.083, Zn = 2.062 and V = 5.185) tend to confirm the structural model

Mise en évidence du couplage ferroélastique-ferroélectrique dans un cristal de structure "bronzes de tungstène quadratiques"

International audienceA crystal with the composition Pb2.07K0.56Nb0.91Ta4.15O15 and having the tungsten bronze structure was grown from a flux. The crystal is pseudotetragonal, orthorhombic (mm2) with a = 17.76 ± 0.01, b = 17.79 ± 0.01, and c = 7.804 ± 0.005 Å. Dielectric and pyroelectric measurements reveal a diffuse ferroelectric-paraelectric transition at 371 ± 5°K. A phase transition occurs at 658 ± 10°K in the paraelec. region. Birefringence measurements show that the biaxial properties, thus the ferroelasticity, vanish at the same temperature Upon application of an elec. field along chosen directions to the polarization vector, a transition from one ferroelastic state (b > a) to another (a > b) was observed, suggesting that the ferroelastic and ferroelec. properties are coupled

Mise en évidence du couplage ferroélastique-ferroélectrique dans un cristal de structure "bronzes de tungstène quadratiques"

International audienceA crystal with the composition Pb2.07K0.56Nb0.91Ta4.15O15 and having the tungsten bronze structure was grown from a flux. The crystal is pseudotetragonal, orthorhombic (mm2) with a = 17.76 ± 0.01, b = 17.79 ± 0.01, and c = 7.804 ± 0.005 Å. Dielectric and pyroelectric measurements reveal a diffuse ferroelectric-paraelectric transition at 371 ± 5°K. A phase transition occurs at 658 ± 10°K in the paraelec. region. Birefringence measurements show that the biaxial properties, thus the ferroelasticity, vanish at the same temperature Upon application of an elec. field along chosen directions to the polarization vector, a transition from one ferroelastic state (b > a) to another (a > b) was observed, suggesting that the ferroelastic and ferroelec. properties are coupled

Contribution à l'étude cristallochimique et optique de silicates et germanates de terres rares appartenant aux systèmes Na2O-(M,M1)III2O3 (M, M'=Nd, Eu, Gd, Er, Al, Bi;X=Si, Ge)-matériaux luminescents et scintillateurs

LA ROCHELLE-BU (173002101) / SudocSudocFranceF

Influence du remplacement du niobium par le molybdène et le tungstène sur les propriétés cristallographiques et diélectriques des phases A2BNb5O15 (A = Sr, Ba ; B = Na, K)

International audienceLe remplacement du niobium par le molybdène ou le tungstène dans les phases A2BNb5O15 (A = Sr, Ba ; B = Na, K) a permis de mettre en évidence six solutions solides de structure "bronzes oxygénés de tugnstène quadratique"..

A new crystal with coupled ferroelastic-ferroelectric properties

International audienceA single crystal Pb2.07K0.56Nb0.91Ta4.15O15 has been grown by the flux method. It crystallizes with the tetragonal tungsten bronze structure. Two transitions have been determined by dielectric, pyroelectric and birefringence measurements: ferroelastic-ferroelectric phase →371 K ferroelastic-paraelectric phase →658 K paraelastic-paraelectric phase. Spontaneous polarization and spontaneous strain are respectively equal to 29 μC · cm-2 and 8 × 10-4 at room temperature. Polar axis is along the [010] direction. Electrical switching of the ferroelastic domains at room temperature shows clearly the existence of a ferroelastic-ferroelectric coupling

Structural relationship between vitreous P2O5 and its relevant crystalline polymorphs by Raman spectroscopy

Vitreous and relevant crystalline polymorphs of P2O5 have been synthesised and characterised by X-ray diffraction and Raman scattering spectroscopy..