# Possible Peierls Distortion Through Re2 Dimer Formation in the LaNiO2‐Type Nitrides LnReN2 (Ln = Pr, Nd)

## TL;DR

Scientists synthesized new nitride materials with unique structures and magnetic properties under high pressure and temperature.

## Contribution

The discovery of LnReN2 materials with distorted LaNiO2-type structures and antiferromagnetic properties.

## Key findings

- Structural distortion in LnReN2 is caused by Re dimerization in the ReN4/2 layers.
- NdReN2 exhibits long-range antiferromagnetic order at 15.5 K.
- The materials combine nitridometallate anions and intermetallic framework features.

## Abstract

Nitride perovskites are a recently opened class of materials with a limited number of stable compounds. Notably, anion‐vacancy‐ordered materials such as LaNiO2‐type nitrides are rare despite useful properties such as superconductivity reported for analogous oxides. Here, we report the preparation of two LnReN2 (Ln = Pr, Nd) materials with a distorted LaNiO2‐type structure at high‐pressure, high‐temperature conditions of a large volume press. Powder X‐ray and neutron diffraction show that the orthorhombic distortion (o‐LnReN2) of the LaNiO2‐aristotype structure is caused by buckling of the ReN4/2 layers through Re dimerization. Electronic structure analysis reveals that the o‐LnReN2 materials are composed of classic nitridometallate anions and a cationic intermetallic framework. Moreover, the calculations reveal the driving force of the Re dimerization likely to be from an electronic instability related to a Peierls‐type distortion. We further characterize the magnetic ground state of both materials with magnetization measurements as well as magnetic neutron scattering uncovering a long‐range antiferromagnetic order of Nd3+ moments in NdReN2 at TN = 15.5 K. The stability of the compounds is investigated by temperature‐dependent powder X‐ray diffraction showing decomposition of NdReN2 at ca. 750 °C. The o‐LnReN2 materials represent a curious class of nitrides at the border of classic nitridometallates, intermetallics, and low‐dimensional complex chemistry.

This study presents the high‐pressure synthesis of two new anion‐vacancy‐ordered perovskite‐related nitrides, PrReN2 and NdReN2, featuring distorted LaNiO2‐type structures. X‐ray and neutron diffraction reveal a structural distortion driven by dimerization of Re‐chains, while electronic structure calculations reveal the simultaneous presence of nitridometallate anions and an intermetallic framework. Magnetic properties were studied with neutron diffraction and magnetization measurements, which reveal an antiferromagnetic ordering of Nd3+ moments in NdReN2 at 15.5 K.