Ba2Zn2B6O13: coplanar [B2O5] in unnoted U-shaped [B6O13] groups achieving large birefringence

Currently, π-conjugated [B2O5] moieties are rarely studied for designing deep-UV birefringent crystals. Here, we report a new deep-UV birefringent crystal Ba2Zn2B6O13 with a deep-UV cut-off edge of 190 nm and large birefringence (Δn = 0.085@ 532 nm), indicating that it can be used as the birefringent material in the DUV area. The first-principles calculation analyses suggest that its large birefringence mainly originates from the coplanar [B2O5] dimers in the unnoted U-shaped [B6O13].