Table Spherical morphologies and hollow structures via hydro(solvo)thermal synthesis. Teflon-lined autoclave and treated at 160 C for specific 30 min under the temperature-controlled mode in a MDS-8 microwave hydrothermal system Praseodymium oxide + nitric acid+ NaF + ammonia + deionized water Placed in a microwave oven (650 W, 2.45 GHz) with a refluxing apparatus. The suspension was heated by microwave irradiation for 20 min at 70% of the maximum power under refluxing.