Аннотация:The search for new materials with pronounced proton or oxygen-ion conductivities is of great importance for the development of solid state ionic and electrochemistry fields. Here, we studied the structure, phase transitions, and ionic (oxygen-ion and proton) conductivity of the pure and Nd containing g-La6W2O15-based composites and pseudorhombohedral La14-xNdxW4O33 (x = 12, 14) solid solutions. The proton conductor La14W4O33 (5 x 10^-5 S/cm at 600 oC) was found to be a two-phase material consisting of an anion-deficient La10W2O21 fluorite-related phase and the g-La6W2O15 orthorhombic phase. The phase content of the pure La10W2O21 cubic phase was ~18 wt% for the g-La6W2O15-based composite. A high degree of Nd content in g-La6W2O15-based composite leads to formation of solid solutions based on a pseudorhombohedral phase in La14-xNdxW4O33 with x = 12 and 14. The Nd-containing g-La6W2O15-based composites exhibited proton conductivity, which gradually decreased with increasing Nd content, whereas La14-xNdxW4O33 (x = 12, 14) pseudorhombohedral solid solutions were identified as oxygen-ion conductors. Nd14W4O33 has the oxygen -ion conductivity of ~4 x 10^-4 S/cm at 700 oC (1.0 x 10^-3 S/cm at 900 oC). In contrast to the g-La6W2O15 phase, the g-La6W2O15-based composite undergoes only a single reversible phase transition at around 910 oC, which can, however, initiate cracks in ceramics. According to DSC and SEM data, the phase transition near 910 oC can be suppressed by introducing Nd into the g-La6W2O15-based composites. The cracking process is enhanced by evaporation of tungsten oxide at T > 1450 oC.