NaYBO: a new rare-earth borate with an infinite one-dimensional [BO] chain and a short ultraviolet cutoff edge.

A new rare-earth borate NaYBO was fabricated by the flux method. The compound crystallizes in the 1̄ group, and shows a three-dimensional network built by [BO] fundamental building blocks (FBBs) with [NaO], [NaO], and [YO] polyhedra. The [BO] FBBs are composed of five planar BO and three BO tetrahedra and connected corner-sharing to construct a unique one-dimensional (1D) [BO] infinity chain that is observed for the first time in the NaO-YO-BO system compound, enriching the structural diversity of rare-earth borate. The title compound exhibits a short ultraviolet (UV) cutoff edge of ∼195 nm and a wide experimental band gap of 5.50 eV. DFT calculations indicate that NaYBO is a direct band gap compound with a calculated GGA band gap of 5.14 eV, and the band gap is mainly determined by B 2p and O 2p orbitals. The results update the phase diagram of NaO-YO-BO and enrich the diversity of rare-earth metal borates.