Oxygen vacancy ordering in superlatives of the two novel oxides, La<SUB>2</SUB>Ni<SUB>2</SUB>O<SUB>5</SUB> and La<SUB>2</SUB>Co<SUB>2</SUB>O<SUB>5</SUB>, prepared by low temperature reduction of the parent perovskites

Controlled reduction of LaBO<SUB>3</SUB>(B=Co or Ni) perovskites gives rise to ordered structures of composition La<SUB>2</SUB>B<SUB>2</SUB>O<SUB>5</SUB>, belonging to the homologous series La<SUB>n</SUB>B<SUB>n</SUB>O<SUB>3n&#8722;1</SUB>, which retain the original features of the perovskite; the co-ordination of the transition metal ions differ, with Ni<SUP>2+</SUP> ions showing octahedral and square-planar co-ordination and the Co<SUP>2+</SUP> ions showing octahedral and tetrahedral co-ordination