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

• We synthesized new phase Bi12.5Lu1.5ReO24.5.
• We measured ion conductivity of Bi12.5Lu1.5ReO24.5.
• We measured formation enthalpy of Bi12.5Lu1.5ReO24.5.
• The phase is thermodynamically stable with respect to decomposition into binary oxides.

The substitution of Re into Bi2O3 allows stabilization of the δ-Bi2O3 structure by additional substitution of lutetium ion to give phase of composition Bi12.5Lu1.5ReO24.5. 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 Bi12.5Lu1.5ReO24.5 at 800 K is the same as the conductivity of BiCuVOx, Bi12.5Ln1.5ReO24.5 (Ln = Eu, La, Nd) phases. In this connection the Bi12.5Lu1.5ReO24.5 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 Bi12.5Lu1.5ReO24.5. For the first time, the standard formation enthalpy of this phase has been determined as follows: ΔfH∘ (Bi12.5Lu1.5ReO24.5, 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 Bi12.5R1.5ReO24.5 (R = Y, La, Nd, Gd, Dy, Lu) phases shown that Bi12.5Lu1.5ReO24.5 is the most thermodynamically stable.