Citation: Pagola, S.; Carbonio, R. E.; Alonso, J. A.; Fernandez-Diaz M T (1997). Crystal structure refinement of Mg Nb2 O6 columbite from neutron powder diffraction data and study of the ternary system MgO-Nb2O5-NbO, with evidence of formation of new reduced pseudobrookite Mg5-xNb4+xO15-d (1.14