Conductivity and hydration of fluorite-type La6 − x WO12 − 1.5x phases (x = 0.4; 0.6; 0.8; 1)

Abstract

Solid phase synthesis was used to obtain four phases from the region of cubic fluorite type La 6 WO 12 -La 10 W 2 O 21 (La 5 WO 10.5 ) solid solution. The temperature dependence of conductivity was mea sured using the impedance spectroscopy technique in the atmosphere of dry ( = 10 -4 atm) and humid ( = 3 × 10 -2 atm) air and also when was varied from 0.21 to 10 -20 atm. Ionic transport numbers t (ion) are calculated (0.6 to 0.9). It was shown that the La 5.6 WO 11.4 phase had a relatively high stability towards hydrolysis, as the value of its conductivity dropped negligibly (as compared to other studied samples) after long-term sample conditioning in a humid atmosphere. Activation energies of hole (0.85 to 0.98 eV) and proton (0.49 to 0.56 eV) conductivity were calculated. The method of thermogravimetric analysis was used to determine the phase hydration degree in the course of cooling from 980 to 200°C at = 3 × 10 -2 atm. Hydration enthalpies ΔH hydr (52 to 67 kJ/mol) were calculated.

Polymorphism in the family of Ln6−xMoO12−δ(Ln = La, Gd–Lu; x = 0, 0.5) oxygen ion- and proton-conducting materials

“…Ln 6 MoO 12 , Ln 6 WO 12 , and solid solutions based on these compounds have recently been the subject of intense research as promising environmentally friendly dyes, luminescent materials, effective catalysts, and oxygen ion and proton conductors. [1][2][3][4][5][6][7][8][9][10][11] Tungstates and molybdates in these series are known to undergo various structural transformations with decreasing Ln ionic radius. The compounds in the Ln 6 WO 12 series have the uorite structure (Fm 3m, no.…”

Structural and transport properties of Nd tungstates and their composites with Ni0.5Cu0.5O obtained by mechanical activation

“…52 The second reason is probably related to blocking the access of the gas carbon dioxide to faster diffusion pathways of the oxide-ionic conductive Ln tungstate/molybdate phase by the adhered nanoparticles of Ni(II) -Cu(II) oxide having a lower oxide ionic conductivity compared to that for the Ln tungstate/molybdate phase. 22,[38][39][40][41] To provide an access to the fluorite phase surface, such a shield of Ni(II)-Cu(II) oxide should be broken. It can be reached by reduction of the sample by hydrogen (in He + H 2 flow at 600 °C for 1 h):…”

Solid oxide proton conductors beyond perovskites

“…Several lanthanide tungstate oxides with a  3:1 Ln2O3 -WO3 molar ratio (Ln = La, Nd, Gd and Er) have been reported to show predominant proton conduction under humidified atmosphere below 900 °C 242,243,244,245,246,247 Please do not adjust margins Please do not adjust margins oxygen vacancies) and are also known as La27W5O55.5-δ, La5.5WO11.25-δ or La6WO12. They exhibit proton transport number of  1 and conductivities of  10 -3 S cm -1 at 600 °C 242,244,248 .…”