Wide band gap of pure ZnO with wurtzite crystal structure (3.1–3.4 eV) limits its photocatalytic activity to the ultraviolet (UV) region of solar spectrum. High-pressure rocksalt polymorph of ZnO can theoretically show narrow band gap; however, the rocksalt phase is unstable at ambient pressure. Herein, rocksalt phase with large fractions of oxygen vacancies is successfully stabilized at ambient conditions by inducing plastic strain in pure ZnO under 6 GPa using the High-Pressure Torsion (HPT) method. Formation of rocksalt phase reduces the band gap of ZnO to 1.8 eV, which is in good agreement with the first-principles calculations, and significantly improves the photocatalytic activity under visible light.

中文翻译：

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窄带隙的高压氧化锌相作为可见光活性光催化剂

具有纤锌矿晶体结构（3.1–3.4 eV）的纯ZnO的宽带隙将其光催化活性限制在太阳光谱的紫外线（UV）区域。ZnO的高压岩盐多晶型物在理论上可以显示出窄的带隙。然而，岩盐相在环境压力下是不稳定的。本文中，通过使用高压扭转（HPT）方法在6 GPa下诱导纯ZnO中的塑性应变，成功地在环境条件下稳定了具有大量氧空位的岩盐相。岩盐相的形成将ZnO的带隙减小到1.8 eV，这与第一性原理的计算非常吻合，并显着提高了可见光下的光催化活性。