Crystal Structure and Physical Properties of Hafnium Boride(HfB2)

Hafnium boride (HfB2) is a new type of ceramic material with high melting point, high thermal conductivity, oxidation resistance and other high-temperature comprehensive properties. It is mainly used in ultra-high temperature ceramics, high-speed aircraft nose cones, aviation, aerospace and other fields. This article will introduce its crystal structure and physical properties, to help explore new applications of this material.

Crystal Structure

The crystal structure of hafnium boride is illustrated in figure 1(a). HfB2 crystallizes in AlB2-type structure with the space group P6/mmm (No. 191), which is isostructural to TiB2 and ZrB2. Specifically, the crystal structure is composed of graphene-like B layers and hexagonal Hf metal layers stacked along the c axis alternatively. The XRD pattern of a single crystal shown in figure 1(b) can be well indexed by the indices of (001) lattice planes. It reveals that the crystal surface is perpendicular to the c axis. The inset of figure 1(b) shows that the crystal has a hexagon shape, consistent with the crystallographic symmetry of hafnium boride^[1].

Figure 1. (a) Crystal structure of HfB2. (b) XRD pattern of a HfB2 single crystal. Inset: photo of a typical HfB2 single crystal.

Physical Properties

A number of theoretical and experimental studies exists in the literature dealing with structural, elastic, and electronic properties of HfB2 and TaB2. Specifically, Shein and Ivanovskii have reported the structural and elastic properties using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for HfB2 and TaB2. Systematic trend in lattice constants and heats of formation have been studied for these compounds by Oguchi. Vajeeston et al. have calculated the electronic structure and ground state properties using the self-consistent tight-binding linear muffin-tin orbital (TB-LMTO) method for same compounds. Kaur et al. have studied the cohesive and thermal properties of these compounds using a rigid ion model (RIM). The simulation results of the electronic structures of HfB2 and TaB2 have been reported by Ivanovskii et al. The bonding nature, elastic property and hardness have been investigated by Zhang et al. for hafnium boride using the first-principles total energy plane-wave pseudopotential (PW-PP) method and reported that, hafnium boride shows a metallic behavior in P6/mmm structure. Hao et al. have investigated the cohesive energy, heat of formation, elastic constant and electronic band structure of HfB2 and TaB2 in the Pmmn space group using the ab initio pseudopotential method^[2].

However, the other physical properties of hafnium boride have received less or none attention. To our knowledge, lattice dynamical and thermodynamical properties, which are the important bulk properties for solids, have not been considered theoretically for these compounds so far^[2].

References

[1] Magnetotransport properties of compensated semimetal HfB2 with high-density light carriers. J. Phys.: Condens. Matter 32 (2020) 015601 (7pp).

[2] Lattice dynamical and thermodynamical properties of HfB2 and TaB2 compounds. doi:10.1016/j.commatsci.2009.11.017