BaPbBO: Structural transformation from a centrosymmetric to a noncentrosymmetric space group by introducing Pb into BaBO

A new congruent-melting lead barium borate, Ba2.5Pb1.5B12O22, was synthesized via a high-temperature solid-state reaction under atmospheric pressure. It crystallizes in the noncentrosymmetric space group Cmc21 with a unit cell of a = 19.051(8) Å, b = 10.726(3) Å, c = 8.612(3) Å, and Z = 4. It features a new functional building block (FBB), [B12O26]16-, that is made up of five [B3O8]7- and one [BO3]3- connected by sharing vertex O atoms. It is derived by introducing Pb into Ba2B6O11, which leads to a structural transformation from a centrosymmetric to a noncentrosymmetric space group. Its second harmonic generation response (SHG) is approximately 0.9 times that of KDP at the fundamental wavelength of 1064 nm and is also phase-matchable. It has a wide transparent region with a UV cutoff edge of about 250 nm according to the reflectance spectra and high thermal stability, which illustrates that it is a potential candidate for ultraviolet nonlinear optical materials.