Na3YB8O15: a new rare-earth borate with an infinite one-dimensional [B8O15]∞ chain and a short ultraviolet cutoff edge

Abstract

A new rare-earth borate Na₃YB₈O₁₅ was fabricated by the flux method. The compound crystallizes in the P group, and shows a three-dimensional network built by [B₈O₁₇] fundamental building blocks (FBBs) with [NaO₆], [NaO₇], and [YO₇] polyhedra. The [B₈O₁₇] FBBs are composed of five planar BO₃ and three BO₄ tetrahedra and connected via corner-sharing to construct a unique one-dimensional (1D) [B₈O₁₅]_∞ infinity chain that is observed for the first time in the Na₂O–Y₂O₃–B₂O₃ 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 Na₃YB₈O₁₅ 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 Na₂O–Y₂O₃–B₂O₃ and enrich the diversity of rare-earth metal borates.