Na 3 YB 8 O 15 : a new rare-earth borate with an infinite one-dimensional [B 8 O 15 ] ∞ chain and a short ultraviolet cutoff edge.

A new rare-earth borate Na 3 YB 8 O 15 was fabricated by the flux method. The compound crystallizes in the P 1̄ group, and shows a three-dimensional network built by [B 8 O 17 ] fundamental building blocks (FBBs) with [NaO 6 ], [NaO 7 ], and [YO 7 ] polyhedra. The [B 8 O 17 ] FBBs are composed of five planar BO 3 and three BO 4 tetrahedra and connected via corner-sharing to construct a unique one-dimensional (1D) [B 8 O 15 ] ∞ infinity chain that is observed for the first time in the Na 2 O-Y 2 O 3 -B 2 O 3 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 Na 3 YB 8 O 15 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 Na 2 O-Y 2 O 3 -B 2 O 3 and enrich the diversity of rare-earth metal borates.