Na2La2B10O19: a new lanthanum sodium borate with infinite 2D layer 2∞[B10O19]8− and moderate birefringence

A new rare earth borate Na2La2B10O19 was successfully synthesized by spontaneous crystallization in a high temperature solution. It crystallizes in the centrosymmetric (CS) space group C2/c with an infinite two-dimensional (2D) double layer which is composed of the fundamental building block (FBB) [B5O12]9−. The calculated birefringence of the compound is 0.06 @1064 nm which mainly originates from the contributions of the B–O anion group according to the first-principles study.