High-Entropy Layered Rare Earth Hydroxides

New high-entropy layered rare earth hydroxides ─ (Y,Eu,Gd,Er,Sm)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Tb)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Yb)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Nd)₂(OH)₅NO₃, and (Y,Eu,Gd,Er,Nd,Sm,Tb)₂(OH)₅NO₃ ─ were obtained using a hydrothermal microwave method. The annealing of layered rare earth hydroxides at 900 °C resulted in the corresponding high-entropy rare earth oxides. Based on inductively coupled plasma atomic emission spectroscopy data, the values for configurational entropy for both rare earth hydroxides and oxides were estimated, confirming the formation of high-entropy compounds. Energy-dispersive X-ray spectroscopy mapping, including mapping in the scanning transmission microscopy mode, showed no signs of chemical segregation and confirmed uniform rare earth elements' distribution both in the particles of high-entropy layered basic nitrates and in the particles of high-entropy oxides. The ratios of rare earth cations in the initial aqueous solutions of mixed nitrates were close to the ratios of cations in the resulting high-entropy layered rare earth basic nitrates and high-entropy rare earth oxides.