Controlling dielectric properties of pyrochlore neodymium zirconate by substitution of rare earth ions

Abstract

The influence of A-site substitution in pyrochlore-type neodymium zirconate with smaller rare earth ions on dielectric properties was investigated. First-principles calculations for [Nd₁₆Zr₁₆O₅₆] and [Nd₁₅MZr₁₆O₅₆] (M = Sm, Gd, Y, Er, or Sc) predicted that Gd, Y, and Er have two types of six equivalent stable positions displaced from the original Nd position, generating a dipole moment. In addition, the energy barrier between these stable positions is below 10⁻² eV, suggesting a potential enhancement of the dielectric constant. To validate the impact of substitution on dielectric properties, (Nd_1−xGd_x)₂Zr₂O₇ (NGZO, x = 0.00, 0.0625, 0.25, 0.50, 0.75, 1.00) and (Nd_1−xEr_x)₂Zr₂O₇ (NEZO, x = 0.00, 0.0625, 0.15, 0.25, 0.50, 0.75, 1.00) were synthesized using the solid-state reaction method. X-ray diffraction confirmed the pyrochlore structure for NGZO (except at x = 1.00) and NEZO (for x ≤ 0.25). The lattice constant followed Vegard’s law within the compositional range of the pyrochlore phase. The dielectric constant slightly increased with increasing x (≤0.25) in NGZO, implying the contribution of dipole moments between Gd and its surrounding O ions.