# New Layered Boride NiPtB2–x (x = 0.5) with a Ternary Derivative Structure of MoB

## TL;DR

A new boride compound, NiPtB2–x, was discovered with a unique layered structure and metallic properties.

## Contribution

The paper introduces a novel ternary boride structure with a new space group and unique atomic arrangements.

## Key findings

- NiPtB2–x has a new structure type with space group Imma and distinct atomic layers.
- The compound exhibits metallic behavior with no phase transitions between 2 and 300 K.
- Boron zigzag chains are stabilized by strong electron contributions from nickel atoms.

## Abstract

A novel ternary boride, NiPtB2–x (x = 0.5), was obtained by argon-arc melting
of
the elements followed by annealing at 750 °C. It exhibits a new
structure type with the space group Imma (a = 2.9835(3) Å, b = 3.0470(3) Å, c = 15.3843(3) Å; Z = 4; single-crystal
X-ray data) and displays distinct layers of condensed [BNi6] and [BPt6] (and [Pt6]) trigonal prisms with
mutually perpendicular axes. Atoms of Pt and Ni from adjacent layers
interlink to form empty tetragonal pyramids and tetrahedra. Two boron
atom positions form two orthogonal zigzag chains; however, one boron
position exhibits a partial boron occupancy. Considering B-deficiency,
the platinum boride substructure in NiPtB2–x quantitatively corresponds to a trigonal prismatic slab in
the Pt2B structure, while the nickel boride partial structure
is consistent with the CrB-type NiB binary. Cell parameters and atomic
coordinates of NiPtB2–x and Pt2B were refined in the scope of generalized gradient approximation.
Chemical bonding analysis by means of the electron localizability
approach, supported by Bader charge analysis, reveals a strong electron
contribution of Ni atoms for stabilization of the boron zigzag chains,
wherein boron atoms are bonded covalently. Bonding within the platinum
boride partial structures in the studied compounds varies depending
on the atom coordination of boron: from covalent in both the NiPtB2–x structure and trigonal prismatic
slabs in Pt2B to mixed metallic with covalent contributions
in [BPt6] octahedra in Pt2B. Electrical resistivity
measurements characterize NiPtB2–x as a metal with no phase transitions in the temperature range from
2 to 300 K, in concord with electronic band structure calculations
and specific heat measurements. The compound is characterized by a
positive Hall coefficient at 20 K. This work unveils a new elemental
space on realizing novel layered boride structural arrangements and
provides a reference for future experiments.

The family of layered borides was extended to NiPtB2−x (space group Imma), a new ternary derivative structure of MoB (space group I41/amd).