Synthesis,structure, and properties of LaSrCuGaO5

The new brownmillerite-related compound, LaSrCuGaO₅, has been synthesized and characterized. It crystallizes in the orthorhombic non-centrosymmetric space group Ima2. The unit cell dimensions are a = 16.383(1) Å, b = 5.5293(7) Å, c = 5.3275(6) Å. The structure is related to perovskite but contains ordered oxygen vacancies within the two-dimensional gallium oxygen layers resulting in tetrahedral coordination of the gallium cations. Other important structural features include buckled copper-oxygen planes, and disorder of the lanthanum and strontium cations over the A-site. Accurate lattice constant measurements reveal an a-axis expansion of 0.17 Å when doped with strontium La_1–xSr_1+xCuGaO₅ (x_max = 0.13). Magnetic susceptibility measurements demonstrate that the compound remains paramagnetic to 4 K.