Metastable ZnO—Lin−2MeOn−1 (Me = Sc3+, Ti4+, Ta5+) solid solutions with a rock-salt structure were synthesized through the solid-state reaction of ZnO with Lin−2Men+On−1 (n = 3, 4, 5) complex oxides at 7.7 GPa and 1300–1500 K. In all investigated systems, single-phase rock-salt solid solutions can be quenched down to ambient conditions in a wide (up to 80 mol% ZnO) concentration range. The phase composition, thermal stability, and thermal expansion of the recovered rock-salt solid solutions were studied by synchrotron powder X-ray diffraction. At ambient pressure, these solid solutions exhibit high thermal stability (up to 1000 K), with the decomposition temperature and decomposition products depending on the nature of the multiple charge cations.