Résumé
Crystals of the Yb-containing double tungstate and double molybdate LiYbX2O8 (X = W, Mo) have been spontaneously grown by a high-temperature flux technique. Their structure has been determined from single-crystal X-ray diffraction at room temperature. LiYbW2O8 crystallizes in the monoclinic P2/n space group (No. 13), with unit cell parameters a = 4.9910(2), b = 5.7964(2), c = 9.8886(4) Å, β = 93.353(1) °. LiYbMo2O8 displays the tetragonal symmetry and is described in the noncentrosymmetric I4̅ space group (No. 82) with a = b = 5.1149(1), c = 11.0919(4) Å. Structural features such as coordination numbers around the atoms and ordered/disordered arrangement of the Yb3+ and Li+ cations explain the differences between these compounds whose vibrational and magnetic properties have also been studied.