# On Chemical Bonding in ht-Ga3Rh and Its Effect on Structural Organization and Thermoelectric Behavior

## TL;DR

This paper studies the crystal structure and thermoelectric properties of a high-temperature form of Ga3Rh, revealing bonding patterns that cause structural disorder and low thermal conductivity.

## Contribution

The paper presents a detailed bonding analysis and structural characterization of the high-temperature Ga3Rh phase, linking its bonding complexity to thermoelectric behavior.

## Key findings

- Ga3Rh exhibits tetragonal symmetry with significant Ga atom disorder indicated by large atomic displacement parameters.
- Quantum chemical analysis reveals Ga–Ga bonds bridging Rh–Rh contacts and absence of Rh–Rh bonding, contributing to structural disorder.
- The compound shows low lattice thermal conductivity (<0.5 W m⁻¹ K⁻¹ at 300 K), linked to its complex bonding.

## Abstract

In the course of systematic studies of intermetallic
compounds
Ga3TM (TM—transition metal), the compound Ga3Rh is synthesized by direct reaction of the elements at 700
°C. The material obtained is characterized as a high-temperature
modification of Ga3Rh. Powder and single-crystal X-ray
diffraction analyses reveal tetragonal symmetry (space group P42/mnm, No. 146) with a = 6.4808(2) Å and c = 6.5267(2)
Å. Large values and strong anisotropy of the atomic displacement
parameters of Ga atoms indicate essential disorder in the crystal
structure. A split-position technique is applied to describe the real
crystal structure of ht-Ga3Rh. Bonding
analysis in ht-Ga3Rh performed on ordered
models with the space groups P1̅, P42nm, and P42212 shows, besides the omnipresent heteroatomic Ga–Rh
bonds in the rhombic prisms ∞3[Ga8/2Rh2], the formation
of homoatomic Ga–Ga bonds bridging the Rh–Rh contacts
and the absence of significant Rh–Rh bonding. These features
are essential reasons for the experimentally observed disorder in
the lattice. In agreement with the calculated electronic density of
states, ht-Ga3Rh shows temperature-dependent
electrical resistivity of a “bad metal”. The very low
lattice thermal conductivity of less than 0.5 W m–1 K–1 at 300 K, being lower than those for most
other Ga3TM compounds, correlates with the enhanced bonding
complexity.

Strong anisotropy of the ADPs of Ga atoms
indicates essential
disorder in the crystal structure of ht-Ga3Rh. Quantum chemical bonding analysis shows besides the omnipresent
heteroatomic Ga−Rh interactions in the main building unit—rhombic
prisms —the formation of homoatomic Ga−Ga
bonds bridging the Rh−Rh contacts and the absence of Rh−Rh
bonding. These features are essential reasons for the experimentally
observed disorder in the lattice and low thermal conductivity.