Cd implantation in α-MoO3: An atomic scale study

Lamellar alpha-MoO3 crystals were implanted with low fluence of radioactive (111)mCd ions at ISOLDE-CERN. Subsequently, we have probed the interaction of the Cd impurity in the lattice with native point defects, such as oxygen vacancies, as a function of annealing temperature using the time differential perturbed angular correlations nanoscopic technique. The experimental data were complemented and interpreted by modeling different Cd-defect configurations in alpha-MoO3 with first-principles density functional theory (DFT). The agreement between experiments and DFT simulations shows that only the interstitial Cd (Cd-I) prevails in the van der Waals gap, by inducing a polaron effect. Upon raising the annealing temperature, Cd-I is able to trap hole charge carriers resultant from the oxygen vacancies VO. Oxygen vacancies were found to form most commonly at two-fold coordinated (O2) atoms. According to comparison DFT results with the experimental electric field gradient values (V-zz and eta) and the calculated formation energies for different defect complexes, the configuration of Cd-I with two (O2) vacancies (V-O2), located at different planes, is found to be more favorable and stable than the other defect configurations. The electron-polaron formation around the Cd impurity at an interstitial site is enhanced by inducing (O2) vacancies with the creation of hole polaron states.

Automated summary

Lamellar alpha-MoO3 crystals were implanted with low fluence of radioactive (111)mCd ions at ISOLDE-CERN. The interaction between Cd impurity and oxygen vacancies in the lattice was studied using the time differential perturbed angular correlations nanoscopic technique. Modeling and simulations confirmed that interstitial Cd prevailed in the van der Waals gap and induced a polaron effect. The most stable defect configuration was found to be Cd-I with two O2 vacancies located at different planes.