Surface reconstructions and stabilization mechanisms have been great challenges for insulators. Based on accurate determination of the long-sought atomic structure of the spinel (1 1 1) surface, here we show that the surface is stabilized by an unconventional mechanism. In general, solid surfaces have unsaturated chemical bonds and are prone to atomic reconstruction to saturate them. The spinel (1 1 1) surface, however, has the surface bonds fully saturated, while the unsaturated bonds remain only in the subsurface. It undergoes a reconstruction that keeps the topmost atomic layer unchanged, but has the subsurface atoms completely rearranged. Such a reconstruction results in a perfect compensation of the surface polarity and a large reduction in the surface energy. This work provides surprising insights into the surface stability and physical and chemical behaviors of complex oxides and insulators.

表面重建和稳定机制一直是绝缘体面临的巨大挑战。基于对尖晶石 (1 1 1) 表面长期寻找的原子结构的准确测定，我们在此表明​​该表面通过非常规机制稳定。通常，固体表面具有不饱和化学键，并且易于进行原子重构以使其饱和。然而，尖晶石 (1 1 1) 表面的表面键完全饱和，而不饱和键仅保留在次表面。它经历了重建，保持最顶层的原子层不变，但地下原子完全重新排列。这种重建导致表面极性的完美补偿和表面能的大幅降低。