Electronic and structural properties, and hyperfine interactions at Sc sites in the semiconductor ${\text{Sc}}_2{\text{O}}_3$: TDPAC and ab initio study

The time-differential $\gamma \text{−}\gamma$ perturbed-angular-correlation (TDPAC) technique using ${}^{44}\text{T}\text{i}\to {}^{44}\text{S}\text{c}$ tracers was applied to study the nuclear quadrupole interaction of the first excited $I=1$ state of ${}^{44}\text{S}\text{c}$ in the cubic bixbyite structure of scandium sesquioxide $\left({\text{Sc}}_2{\text{O}}_3\right)$. In addition, ab initio calculations of electronic and structural properties and hyperfine parameters at the cationic sites of the ${\text{Sc}}_2{\text{O}}_3$ structure were performed using the full-potential augmented plane wave plus local-orbital $\left(\text{APW}+\text{lo}\right)$ method. The accuracy of the calculations and the excellent agreement of the predicted electric-field-gradient (EFG) tensors and the structural properties (lattice parameters, internal positions) with the experimental results enable us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC experiments. Additionally, the $\text{APW}+\text{lo}$ calculations show that the EFG at Sc sites is originated in the population of $\text{Sc}3p$ states and give an explanation for the preferential occupation of the asymmetric cationic site $C$ of the structure by the ${}^{44}\text{T}\text{i}$ doping impurities. Finally, the validity of the ionic model, usually used to describe the EFG at native cation sites, is discussed.

Figure 1

(a) Idealized crystal structure of ${\text{Sc}}_2{\text{O}}_3$. Note two types of octahedral cation sites in alternating layers. (b) Nearest-neighbor oxygen (gray spheres) distribution around each cationic site (black spheres) in the bixbyite structure.

Figure 2

$R\left(t\right)$ spectrum (left) and their corresponding cosine transform (right) of $\left({}^{44}\text{T}\text{i}\to \right){}^{44}\text{S}\text{c}$ in cubic ${\text{Sc}}_2{\text{O}}_3$ measured at 300 K. The frequencies ${\omega }_n$ associated with the hyperfine interactions HFIC and HFID are indicated in the Fourier spectrum.

Figure 3

Calculated band structure for the system ${\text{Sc}}_2{\text{O}}_3$. Zero energy is at the Fermi level $\left(E_F\right)$, denoted by a solid horizontal line.

Figure 4

Calculated total and partial densities of states of ${\text{Sc}}_2{\text{O}}_3$. Energies are referred to the Fermi level $\left(E_F\right)$, denoted by a vertical dashed line.