Preparation, ionic conductivity and thermochemistry of new Bi12.5Lu1.5ReO24.5 phase

Abstract

• We synthesized new phase Bi 12.5 Lu 1.5 ReO 24.5 . • We measured ion conductivity of Bi 12.5 Lu 1.5 ReO 24.5 . • We measured formation enthalpy of Bi 12.5 Lu 1.5 ReO 24.5 . • The phase is thermodynamically stable with respect to decomposition into binary oxides. The substitution of Re into Bi 2 O 3 allows stabilization of the δ-Bi 2 O 3 structure by additional substitution of lutetium ion to give phase of composition Bi 12.5 Lu 1.5 ReO 24.5 . The phase was synthesized for the first time. Structural analysis performed by neutron diffraction showed that space group was Fm3m with lattice parameter a = 5.5591(2) Ǻ. The phase has been found to show high ion conductivity at moderate temperature. The conductivity was measured in the temperature range of 600–800 K. The conductivity of Bi 12.5 Lu 1.5 ReO 24.5 at 800 K is the same as the conductivity of BiCuVO x , Bi 12.5 Ln 1.5 ReO 24.5 (Ln = Eu, La, Nd) phases. In this connection the Bi 12.5 Lu 1.5 ReO 24.5 phase offers excellent potential for moderate temperature application. Solution calorimetry, using 2.0 M HCl ( T = 298.15 K) as a solvent, was used to study the thermochemistry of Bi 12.5 Lu 1.5 ReO 24.5 . For the first time, the standard formation enthalpy of this phase has been determined as follows: Δ f H ∘ (Bi 12.5 Lu 1.5 ReO 24.5 , s, 298.15 K) = −5819.4 ± 8.2 kJ/mol. The thermodynamic stability at room temperature has been assessed. The results show that investigated phase is thermodynamically stable with respect to binary oxides. Comparing the formation enthalpies from binary oxides for Bi 12.5 R 1.5 ReO 24.5 (R = Y, La, Nd, Gd, Dy, Lu) phases shown that Bi 12.5 Lu 1.5 ReO 24.5 is the most thermodynamically stable.