Preparation and properties of high-entropy rare earth niobate LnNbO4 microwave dielectric ceramics

The impact of configurational entropy on the microwave dielectric properties of LnNbO 4 fergusonite was investigated by designing a series of high-entropy counterparts, including (La, Nd, Sm, Ho, Yb, Y)NbO 4 (6RNO), (La, Nd, Sm, Eu, Ho, Yb, Y)NbO 4 (7RNO), (La, Nd, Sm, Eu, Gd, Ho, Yb, Y)NbO 4 (8RNO), and (La, Nd, Sm, Eu, Gd, Ho, Tm, Yb, Lu, Y)NbO 4 (10RNO). Simply prepared by the solid-state route, a pure phase with a monoclinic fergusonite structure of space group C /2 c was obtained. By comparing the microstructural evolution and lattice vibration modes, an analysis was conducted on the variations in microwave dielectric performances. It was confirmed that the permittivity ( ε r ) is primarily influenced by relative density, while the quality factor ( Q  ×  f ) exhibits a strong correlation with packing fraction and lattice vibrations. The resonant frequency temperature coefficient (τ f ) is significantly associated with bond valence. The optimal microwave dielectric properties were achieved in 7RNO ceramics at a temperature of 1270 °C, resulting in a relative density of 95.43 %. The microwave dielectric properties were measured as ε r  = 18.62, Q  ×  f  = 35200 GHz, τ f  = −23.28 ppm/°C. The present study expands the application of entropy engineering to achieve ultrahigh configurational entropy in microwave dielectric ceramics . These findings demonstrate that optimizing the configuration entropy is an effective approach for manipulating the dielectric properties, thereby providing valuable insights for material component design.