“…16 In the 1980s, D-J phases were found and represented as the general formula as M[A n-1 B n O 3n+1 ] where M : alkali metal, A : alkaline or rare earth metal, B : transition metal, and n : the number of perovskite layers. 19 D-J-types such as KTiNbO 5 , 20 RbLaTa 2 O 7 , 21 CsBa 2 Ta 3 O 10 , 22 and especially, KCa 2 Nb 3 O 10 , have gained a lot of attention owing to the fabrication of layered perovskite nanosheets. [23][24][25][26] Potassium calcium niobate is also classified as a group of layered niobium oxides because of the existence of niobium in the component.…”