Potassium- and Lithium-Ammonia Intercalation into Excitonic Insulator Candidate Ta2NiSe5.

Abstract

Two new reduced phases derived from the topical excitonic insulator candidate Ta2NiSe5 have been synthesized via the intercalation of lithium and potassium from solutions of the metals in liquid ammonia. Li(NH3)Ta2NiSe5 and KTa2NiSe5 both crystallize in orthorhombic space group Pmnb with the following lattice parameters: a = 3.5175(1) Å, b = 18.7828(7) Å, and c = 15.7520(3) Å and a = 3.50247(3) Å, b = 13.4053(4) Å, and c = 15.7396(2) Å, respectively. They have increased unit cell volumes of 48% and 31%, respectively, relative to that of Ta2NiSe5. Significant rearrangement of the transition metal selenide layers is observed in both intercalates compared to the parent phase. In Li(NH3)Ta2NiSe5, neutron diffraction experiments confirm the location of the light Li, N, and H atoms, and solid-state nuclear magnetic resonance (NMR) experiments show that H, N, and Li each occupy a single environment at ambient temperature on the NMR time scale. Magnetometry data show that both intercalates have increased magnetic susceptibilities relative to that of Ta2NiSe5, consistent with the injection of electrons during intercalation and an enhancement of the Pauli paramagnetism.