Boldú, J., J. Barreto, I. Rosales, L. Bucio, and E. Orozco. “XPS, DRUV-VIS and ESR Characterization of the Non-Stoichiometric Compound Ge$_{0.74}$V$_{0.21}$ $\square_{0.05}$O$_{2}$”. Revista Mexicana De Física, vol. 63, no. 2 Mar-Apr, Jan. 2017, pp. 166-0, https://rmf.smf.mx/ojs/index.php/rmf/article/view/329.