Potassium–\nand Lithium–Ammonia Intercalation\ninto Excitonic Insulator Candidate Ta<sub>2</sub>NiSe<sub>5</sub>

Two new reduced phases derived from the topical excitonic\ninsulator\ncandidate Ta<sub>2</sub>NiSe<sub>5</sub> have been synthesized via\nthe intercalation of lithium and potassium from solutions of the metals\nin liquid ammonia. Li(NH<sub>3</sub>)Ta<sub>2</sub>NiSe<sub>5</sub> and KTa<sub>2</sub>NiSe<sub>5</sub> both crystallize in orthorhombic\nspace group <i>Pmnb</i> with the following lattice parameters: <i>a</i> = 3.5175(1) Å, <i>b</i> = 18.7828(7) Å,\nand <i>c</i> = 15.7520(3) Å and <i>a</i> =\n3.50247(3) Å, <i>b</i> = 13.4053(4) Å, and <i>c</i> = 15.7396(2) Å, respectively. They have increased\nunit cell volumes of 48% and 31%, respectively, relative to that of\nTa<sub>2</sub>NiSe<sub>5</sub>. Significant rearrangement of the transition\nmetal selenide layers is observed in both intercalates compared to\nthe parent phase. In Li(NH<sub>3</sub>)Ta<sub>2</sub>NiSe<sub>5</sub>, neutron diffraction experiments confirm the location of the light\nLi, N, and H atoms, and solid-state nuclear magnetic resonance (NMR)\nexperiments show that H, N, and Li each occupy a single environment\nat ambient temperature on the NMR time scale. Magnetometry data show\nthat both intercalates have increased magnetic susceptibilities relative\nto that of Ta<sub>2</sub>NiSe<sub>5</sub>, consistent with the injection\nof electrons during intercalation and an enhancement of the Pauli\nparamagnetism.