The discovery of new topological electronic materials brings a chance to uncover new physics. Up to now, many materials have been theoretically proposed and experimentally proved to host different kinds of topological states. Unfortunately, there is little convincing experimental evidence for the existence of topological oxides. The reason is that oxidation of oxygen leads to ionic crystal in general and makes band inversion unlikely. In addition, the realization of different topological states in a single material is quite difficult, but strongly needed for exploring topological phase transitions. In this work, using first-principles calculations and symmetry analysis, we propose that the experimentally tunable continuous solid solution of oxygen in pyrochlore Tl₂Nb₂O_6+x (0 ≤ x ≤ 1.0) leads to various topological states. Topological insulator, Dirac semimetal, and triply degenerate nodal point semimetal can be realized in it via changing the oxygen content and/or tuning the crystalline symmetries. When x = 1, it is a semimetal with quadratic band touching point at Fermi level. It transits into a Dirac semimetal or a topological insulator depending on the in-plane strain. When x = 0.5, the inversion symmetry is spontaneously broken in Tl₂Nb₂O_6.5, leading to triply degenerate nodal points. When x = 0, Tl₂Nb₂O₆ becomes a trivial insulator with a narrow band gap. These topological phase transitions driven by solid solution of oxygen are unique and physically plausible due to the variation of valence state of Tl⁺ and Tl³⁺. This topological oxide will be promising for studying correlation induced topological states and potential applications.

新拓扑电子材料的发现为发现新物理提供了机会。到目前为止，理论上已经提出了许多材料，并通过实验证明它们具有不同的拓扑状态。不幸的是，几乎没有令人信服的实验证据表明存在拓扑氧化物。原因是氧气的氧化通常会导致离子晶体，并使能带反转不太可能。另外，在单一材料中实现不同拓扑状态非常困难，但是探索拓扑相变非常需要。在这项工作中，我们使用第一性原理计算和对称性分析，提出了在烧绿石中Tl ₂ Nb ₂ O _6+X（0≤  X  ≤1.0）导致各种拓扑状态。通过改变氧含量和/或调节晶体对称性，可以在其中实现拓扑绝缘体，狄拉克（Dirac）半金属和三重简并的结点半金属。当x  = 1时，它是半金属，费米能级上具有二次带接触点。根据面内应变，它会转变为Dirac半金属或拓扑绝缘体。当x  = 0.5时，反演对称性在Tl ₂ Nb ₂ O _6.5中自然破裂，导致三重简并的结点。当x  = 0时，Tl ₂ Nb ₂ O ₆变成了一个窄带隙的琐碎绝缘子。由于Tl ⁺和Tl ³⁺的化合价态的变化，由氧的固溶体驱动的这些拓扑相变是独特的，并且在物理上似乎是合理的。这种拓扑氧化物将有望用于研究相关诱导的拓扑状态和潜在的应用。