Novel synthesis of the layer structured β-ZrNCl by the direct reactions of zirconium metal or zirconium hydride with ammonium chloride

Two different polymorphs of the metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) are known to crystallize in layered structures. The two crystal structures differ in the way 2 ∞ {X[M 2 N 2 ]X} slabs are stacked along the c-axes. Metal atoms and/or organic molecules can be inter- calated into the van-der-Waals gap between these layers. After such an electron-doping via intercalation the prototypic band insulators change into superconductors with moderate high critical temperatures T c up to 25.5 K. This review gathers information on synthesis routes, structural characteristics and properties of the prototypic nitride halides and the derivatives after electron-doping with a focus on superconductivity.

Superconducting nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

The layered nitrides β-MNX (M = Zr, Hf; X = Cl, Br) crystallize in the space group R3m with a hexagonal cell of dimensions a = 3.6031(6) A, c = 27.672(2) A for β-ZrNCl, a = 3.5744(3) A, c = 27.7075(9) A for β-HfNCl, and a = 3.6379(5) A, c = 29.263(2) A for β-ZrNBr. Lithium intercalation using n-buthyllithium in hexane solutions leads to solvent free superconductors of formula Li0.20ZrNCl, Li0.42HfNCl, Li0.67HfNCl, and Li0.17ZrNBr showing critical temperatures of 12, 18, 24, and 13.5 K, respectively. Whereas several samples of β-ZrNBr and β-ZrNCl showed reproducibility in the lithium uptake and in the corresponding critical temperatures, different samples of β-HfNCl subjected to the same treatment in n-buthyllithium showed lithium uptakes ranging from 0.07 to 0.67, and corresponding critical temperatures between 0 and 24 K. A linear dependence of Tc versus the lithium content is observed when all the superconducting samples are considered. The results obtained from electrochemical lithiation are consisten...

Chemical Transport Synthesis, Electrochemical Behavior, and Electronic Structure of Superconducting Zirconium and Hafnium Nitride Halides.

We report evidence for superconductivity induced by the application of strong electric fields onto the surface of a band insulator, ZrNCl, provided by the observation of a shielding diamagnetic signal. We introduced an electric-double-layer capacitor configuration and in situ magnetization measurements at low temperatures as a method to detect the novel electric-field-induced superconducting state. The results showed excellent agreement with a previous report using a transistor configuration, demonstrating that the present technique is a novel method for investigating the nonequilibrium phase induced by electric fields.

Electric-Field-Induced Superconductivity Detected by Magnetization Measurements of an Electric-Double-Layer Capacitor

Hydrogen is taken up by a layer structured compound β-ZrNCl during its chemical vapor transport with NH4Cl in a sealed silica tube. The transported sample can be further hydrogenated by hydrogen spillover, and dehydrogenated by oxidation with Cl2 and KMnO4. The infrared absorption spectra indicate that the hydrogen is taken up in the double ZrN layer of β-ZrNCl, coordinating to a nitrogen atom. The second moments of 1H-NMR spectra suggest the formation of hydrogen pairs in β-ZrNCl. A motional line narrowing of the 1H-NMR spectrum was observed at temperatures around 200 K. The activation energy for the jumping motion of the hydrogen was determined to be 10.6 kJ/mol from the temperature dependence of the spin-lattice relaxation time. A possible structural model for the location of hydrogen was proposed.

1H-NMR STUDY OF HYDROGEN INTERCALATED IN β-ZIRCONIUM NITRIDE CHLORIDE

A layer structured crystal β-zirconium nitride chloride ZrNCl has been found to form a new lithium intercalate. The intercalation occurs either by the n-butyl lithium technique or by electrochemical redox reactions. The layer crystal exhibits electrochromic behavior on intercalation-deintercalation of the lithium.

SumiharaMasanori

Papers

LITHIUM INTERCALATION AND ELECTROCHROMISM IN β-ZrNCl LAYERED CRYSTAL