Description
MoO3 is a promising material for applications in sensors and future electrochromic imaging devices. Since the phenomenology at the origin of the macroscopic properties occurs at the atomic scale, we used the nuclear technique of Perturbed Angular Correlation (PAC), after implantation of 111mCd or 176Lu at ISOLDE, on MoO3 samples to investigate the defect structure and recovery upon ion implantation and subsequent annealing, as well as the site occupancy of the implanted impurity. Cd in MoO3 is intended to be an electrical dopant and may improve the transport properties of this material, while rare earth doping is investigated for their light emission characteristics. The samples studied were α-MoO3 single crystals grown by a sublimation method. The PAC measurements were carried out as a function of temperature in air after annealing at 450° C also under air for 20 min. Raman measurements were carried out at room temperature by using a 633 nm He–Ne laser as the excitation source, and reveal a high crystalline quality that is not affected by annealing treatments in air up to 450 0C. After annealing, two Electric Field Gradients distributions are observed, which for 37 % of the 111mCd atoms are characterized by a fundamental frequency ω01 = 247 Mrad/s with an asymmetry parameter of 0.484 and negligible frequency distribution. The remaining fraction is characterized by ω02 = 212.98 (4.69) Mrad/s and a wide frequency distribution that we assume to be due to a fraction of probes incorporated in damaged – non-annealed sites in the crystal. The well-defined quadrupole frequencies observed are the evidence for Cd and Lu occupying a limited number of lattice sites in the host. Also, it was found that a low temperature is required to anneal defects and place an important fraction of the impurity atoms in relatively regular sites, with no defects in their neighborhood. Actually, it is not clear if the wide distribution of EFGs found for the biggest fraction of probing atoms is due to intrinsic defects on the crystals or from a not-optimized annealing procedure. PAC has shown to be a powerful technique to probe the incorporation of potential impurity dopants upon temperature measurements and systematic studies are envisaged.
Primary authors
Dr
Carlos Díaz-Guerra
(Dpto. Física de Materiales, Facultad de Ciencias Físicas, Universidad Complutense de Madrid)
Dr
Joao Guilherme Martins Correia
(Centro de Ciências e Tecnologias Nucleares (PT))
Dr
Katharina Lorenz
(Instituto Superior Técnico, Lisboa University (PT))
