Engineering the Spin Transition and Carrier Type with High-Entropy Lattice Distortions in Rare Earth Cobaltates

There is growing interest in material candidates that provide knobs to tune their properties beyond traditional limits. Compositionally complex oxides, often called high entropy oxides, are excellent candidates, wherein a lattice site shares more than four cations, forming single-phase solid solutions with unique properties. Here, we demonstrate compositional complexity as a tunable parameter in a spin-transition oxide semiconductor La_1-x(Nd,Sm,Gd,Y)_xCoO₃, by varying the population x of rare earth cations.  As the compositional complexity increases with x, localized and uniform lattice distortions occur that have profound effects on the material’s semiconductor-to-metal spin transition and carrier type. Experimental measurements, together with first-principles calculations, demonstrate that atomic-range distortions from the varying rare earth radii induce a crossover from hole-majority to electron-majority conduction at x = 0.8 without the introduction of electron donors. Thus, we show that control of localized lattice distortions through compositional complexity is a facile knob to tune oxide semiconductors and spin transitions beyond traditional means.