Site localization of Cd impurities in sapphire

G. N. DARRIBA; M. RENTERÍA; H. M. PETRILLI

San Pablo

Workshop; II Workshop do Instituto Nacional de Eletrônica Orgânica - INEO; 2010

INEO

The Al2O3 in the corundum phase has a variety of technological applications such as high temperature structural ceramics, dielectric insulators, optical devices and thin film technology [1-8]. Many of these properties are closely related to point defect and impurities introduced in bulk Al2O3. One of the most important motivations is that Al2O3 is a promising candidate for a new generation of emissive optical materials, making use of isolated impurities in ceramic matrices. Future higher communication rates and greater data density will likely depend on new rare earth ion hosts where the local environment is manipulated to alter the optical behavior. Single electric-field gradient (EFG) obtained from γ-γ Perturbed Angular Correlation (PAC) experiments at 111In/111Cd impurity sites in a-Al2O3 have been already reported in the literature. In these works the hyperfine interaction observed are assigned to Cd probes localized at substitutional cation  sites in the corundum structure [9-10]. Nevertheless, other authors [11] claimed that Cd could be localized at interstitial sites. In this work we present a theoretical study of  Cd impurities in a-Al2O3 using ab initio calculations for different impurity charge states and site localizations (substitutional and interstitial)  and compare the EFG results (in magnitude, orientation and symmetry) with the experimental ones. The structural relaxations and electronic properties induced by the presence of the Cd impurity in both sites (substitutional and interstitial) in the a-Al2O3 lattice are discussed too. The ab initio calculations were performed with the FP-APW+lo (Full-Potential Augmented Plane Wave plus Local Orbitals) and PAW (Projector Augmented Wave) methods, both in the framework of the Density Functional Theory, using WIEN2K and CP-PAW codes, respectively. From the comparison between theory and experiment both substitutional and interstitial scenarios for Cd atoms are possible. Finally, future possible experiments are discussed that could resolve these ambiguity.   [1] R. M. Cannon, W. H. Rhodes, and A. H. Heuer, J. Am. Ceram. Soc. 63, 46 (1980). [2] A. H. Heuer, N. J. Tighe, and R. M. Cannon, J. Am. Ceram. Soc. 63, 53 (1980). [3] K. P. D. Lagerlöf, T. E. Mitchell, and A. H. Heuer, J. Am. Ceram. Soc. 72, 2159 (1989). [4] A. H. Heuer and K. P. D. Lagerlöf, Philos. Mag. Lett. 79, 619 (1999). [5] X. Tang, K.P.D. Lagerlöf, and A.H. Heuer, J. Am. Ceram. Soc. 86, 560 (2003). [6] H. Shoshida, Y. Ikuhara, and T. Sakuma, Acta Mater. 50, 2955 (2002). [7] B. D. Evans, J. Appl. Phys. 70, 3995 (1991). [8] R. H. French and A. H. Heuer, J. Am. Ceram. Soc.77, 292 (1994). [9] S. Habenicht, D. Lupascu, M. Neubauer, M. Uhrumacher, K.P. Lieb and the ISOLDE-Collaboration, Hyp. Int.120/121, 445-448, (1999). [10] J. Penner and R. Vianden, Hyp. Int. 158, 389-394, (2005). [11] J.G. Marquez, A.A. Melo, J.C. Soares, E. Alves, M.F. da Silva, K. Freitag, Nucl. Instr. And Meth. In Phys. Res B 106, 602-605, (1995).