Zintl compounds make excellent thermoelectrics with many opportunities for chemically tuning their electronic and thermal transport properties. However, the majority of Zintl compounds are persistently p-type even though computation predicts superior properties when n-type. Surprisingly, n-type Mg₃Sb₂-based thermoelectrics have been recently found with exceptionally high figure of merit. Excess Mg is required to make the material n-type, prompting the suspicion that interstitial Mg is responsible. Here we explore the defect chemistry of Mg₃Sb₂ both theoretically and experimentally to explain why there are two distinct thermodynamic states for Mg₃Sb₂ (Mg-excess and Sb-excess) and why only one can become n-type. This work emphasizes the importance of exploring all of the multiple thermodynamic states in a nominally single-phase semiconductor. This understanding of the existence of multiple inherently distinct different thermodynamic states of the same nominal compound will vastly multiply the number of new complex semiconductors to be discovered for high zT thermoelectrics or other applications.

Zintl化合物可制成出色的热电材料，并具有许多化学调节其电子和热传输性质的机会。然而，即使计算预测当n-型时具有优异的性质，大多数Zintl化合物仍是p-型。令人惊讶地，最近发现基于n型Mg ₃ Sb ₂的热电材料具有极高的品质因数。要使材料成为n型，就需要过量的Mg ，这促使人们怀疑间隙Mg是造成这种情况的原因。在这里我们探索Mg ₃ Sb ₂的缺陷化学从理论上和实验上都解释了为什么Mg ₃ Sb ₂有两个不同的热力学状态（过量Mg和过量Sb），以及为什么只有一个能变成n型。这项工作强调了探索标称单相半导体中所有多个热力学状态的重要性。对相同标称化合物存在多个固有不同的不同热力学状态的理解将极大地增加要为高zT热电学或其他应用发现的新型复杂半导体的数量。