Stabilisation of Ba2CuO2Cl2 with the K2NiF4 structure by chemical substitution

Abstract

The hitherto unknown compound Ba₂CuO₂Cl₂ in which the Ba atoms occupy the A sites of the K₂NiF₄-type structure, has been stabilised by chemical doping mechanisms. It is found that a small amount (20–25%) of Ca or Cd substituted for Cu was instrumental in this stabilisation. The least-squares fitted tetragonal lattice parameters of the new phases, Ba₂(Cu_0.80M_0.20)O₂C1₂(M = Ca, Cd) are a= 4.1779(1), c= 16.2303(2)Å and a= 4.1721(1), c= 16.2298(1)Å, respectively. They are found to follow the trend exhibited by the other known A₂CuO₂Cl₂ compounds (A = Ca, Sr). Rietveid analysis confirmed that the substituted ions are distributed randomly at the six-coordinated Cu sites of the K₂NiF₄ structure. The stabilisation mechanism has been explained in terms of the crystallographic tolerance factor criteria and structural requirements needed for the formation of layered structures involving Ba and Cu.