A synthetic route has been discovered to thermodynamically unstable, i.e., metastable, Sn(II)–perovskite oxides that have been highly sought after as lead-free dielectrics and small bandgap semiconductors. A highly facile exchange of Sn(II) is found by using a low melting SnCl₂/SnF₂ peritectic flux, yielding mixed A-site (Ba_1–xSn_x)ZrO₃ and mixed A- and B-site (Ba_1–xSn_x)(Zr_1–yTi_y)O₃ solid solutions that exhibit a very high metastability, with up to 60% Sn(II) cations and a calculated reaction energy for decomposition of up to −0.3 eV atom^–1. Kinetic stabilization of the higher Sn(II) concentrations is achieved by the high cohesive energy of the perovskite compositions containing Zr(IV) and mixed Zr(IV)/Ti(IV) cations. Significantly red-shifted bandgaps are found with increasing Sn(II) substitution, enabling the optical absorption edge to be broadly tuned from ∼3.90 to ∼1.95 eV. Percolation pathways are calculated to occur for BSZT compositions with >12.5% Sn(II) and >25% Ti(IV) cations. High photocatalytic rates are found for molecular oxygen production for compositions which exceed the percolation thresholds, wherein extended diffusion pathways should “open up” across the structure and the charge carriers become delocalized rather than trapped. These results establish the critical importance of synthetically accessing metastable semiconductors for the discovery of advanced optical and photocatalytic properties.

中文翻译：

---

推动半导体钙钛矿氧化物在可见光驱动水氧化中的亚稳性极限

已经发现一种合成途径可以解决热力学不稳定的问题，即亚稳态的Sn（II）-钙钛矿氧化物，是无铅电介质和小带隙半导体的追捧者。通过使用低熔点的SnCl ₂ / SnF ₂包晶熔剂，可以很容易地交换Sn（II），产生混合的A部位（Ba _{1– x} Sn _x）ZrO ₃以及混合的A部位和B部位（Ba _{1 – x} Sn _x）（Zr _{1 – y} Ti _y）O ₃固溶体，具有非常高的亚稳性，具有高达60％的Sn（II）阳离子和计算得出的分解至-0.3 eV原子的反应能^–1。较高的Sn（II）浓度可通过含有Zr（IV）和Zr（IV）/ Ti（IV）混合阳离子的钙钛矿组合物的高内聚能实现动力学稳定。随着Sn（II）取代的增加，发现明显的红移带隙，使光吸收边缘可从约3.90 eV宽泛调整至约1.95 eV。计算出具有> 12.5％Sn（II）和> 25％Ti（IV）阳离子的BSZT组合物发生的渗透途径。对于超过渗滤阈值的组合物，发现分子氧产生的光催化速率较高，其中扩展的扩散途径应在结构上“打开”，并且载流子变得离域而不是被俘获。