A hard open-framework iron-based boride semiconductor synthsized - Dr. Huiyang Gou and Dr. Jun Deng

New research led by Dr. Huiyang Gou and Dr. Jun Deng at the Center for High Pressure Science and Technology Advanced Research (HPSTAR), in collaboration with national and international researchers, reports the successful synthesis and comprehensive characterization of FeSiB₂, a previously unrecognized ternary iron silico-boride with an open-framework structure. This material exhibits n-type semiconducting behavior, excellent mechanical performance, and a nearly isotropic elastic response, arising from its three-dimensional covalently bonded Si–B framework. The study was published in the Journal of the American Chemical Society under the title “FeSiB₂ : A Hard Semiconducting Open-Framework Iron Silico-Boride.”

Open-framework inorganic materials have attracted broad interest due to their low density, structural tunability, and interconnected channels, which enable diverse electronic and optical functionalities. Metal silico-borides are a promising platform for such architectures, but reported systems have largely been limited to alkali or alkaline-earth metals. Extending these frameworks to 3d transition metals is highly challenging, as these systems typically favor densely packed structures.

Using a high-pressure, high-temperature melt-mediated synthesis strategy, co-first author Dr. Junkai Li explained that the team overcame the intrinsic thermodynamic preference for dense phases and successfully obtained high-quality FeSiB₂ crystals. Structural analysis shows that FeSiB₂ crystallizes in a monoclinic P2_₁/c structure, featuring a three-dimensional covalent Si–B framework with Fe atoms occupying interstitial sites. Co-first author Dr. Wenju Zhou added that this framework remains robust from 30 K to room temperature and maintains structural stability under compression up to 52.9 GPa. Transmission electron microscopy revealed a localized four-layer modulated structure, which does not affect the primary structural features.

Electrical transport measurements confirm n-type semiconducting behavior. First-principles calculations indicate that the bandgap originates from crystal field splitting of Fe-d orbitals, while B–B, Si–B, and Si–Si covalent bonds form a three-dimensional network with Fe acting as an electron donor. This covalent network underpins excellent mechanical performance, with a Vickers hardness of 22.6 GPa, bulk modulus of 211(7) GPa, and Young’s modulus of 362.7(25) GPa, comparable to most transition-metal borides. Importantly, unlike many conventional transition-metal borides, FeSiB₂ exhibits a nearly isotropic elastic response, attributed to a balanced bond-strength distribution within the Si–B framework.

This work demonstrates that complex open-framework architectures can be stabilized even in transition-metal boride systems that are strongly biased toward dense structures. By connecting synthesis pathways, local structural modulation, semiconducting behavior, and mechanical performance, the study expands the structural and functional landscape of silico-borides and provides a new route toward hard open-framework materials.

Caption: Crystal structure of FeSiB₂ an open-framework iron silico-boride with semiconducting behavior and a nearly isotropic mechanical response.

近日，研究人员成功制备并系统表征了一种具有开放骨架结构的硬质三元铁基硅硼化物FeSiB₂。作为过渡金属硼化物家族中的新成员，FeSiB₂ 突破了硼化物偏好致密堆积结构的传统认知，展现出由三维Si–B共价网络与填隙Fe原子构成的单斜开放骨架结构，并兼具n型半导体行为以及近各向同性的弹性响应。围绕这一新材料，北京高压科学研究中心缑慧阳团队联合国内外合作者，采用高压高温熔融介导合成策略，结合常压和高压单晶X射线衍射、原位大腔体压机、透射电子显微镜、电输运测试、纳米压痕及第一性原理计算等手段，揭示了FeSiB₂ 从过饱和熔体中快速结晶的形成机制和在较高温压下优异的结构稳定性，并阐明了其半导体特性和各向同性力学响应的微观机制。该工作揭示了在传统上偏好致密结构的过渡金属硼化物体系中，借助高压熔融策略可稳定复杂开放骨架结构并赋予其新颖功能特性，为新型硬质开放骨架型材料的探索及硅硼化物家族的拓展提供了新方向。相关成果近日在线发表于《美国化学会志》(https://doi.org/10.1021/jacs.6c00948)。