Oxygen Vacancy and Grain‐Boundary Space Charge in Mn‐Doped CaZrO ₃ Ceramics Sintered in a Reducing Atmosphere

ABSTRACT CaZrO 3 is a chemically robust perovskite dielectric that is attractive for multilayer ceramic capacitors co‐fired with base‐metal electrodes, but its properties under reducing conditions are governed by oxygen‐vacancy–related defects. In this work, CaZrO 3 ceramics with 0, 0.2, and 0.5 mol% MnO were prepared by solid‐state reaction and sintered in N 2 . x‐Ray diffraction and Rietveld refinement show single‐phase orthorhombic CaZrO 3 for all compositions, with a slight decrease in lattice parameters and B–O bond lengths consistent with Mn 2+ substitution on the Zr 4+ (B) site. Dilatometry, density, and SEM reveal that Mn strongly promotes densification: nearly full density (∼99%) and modest grain growth are obtained at 1400°C for 0.5 mol% MnO. Photoluminescence and EPR show that Mn doping introduces a g ≈ 2 resonance whose intensity and linewidth increase with MnO content, confirming the formation of Mn 2 + and associated oxygen‐vacancy–related centers. The disappearance of the V O • ‐like shoulder at higher Mn levels indicates that oxygen vacancies increasingly form strongly coupled or EPR‐silent complexes, reflecting a systematic evolution of the defect landscape with Mn addition. Low‐temperature dielectric spectroscopy and Arrhenius analysis of the AC conductivity yield activation energies of ∼0.49 eV for undoped CaZrO 3 and 0.18 eV for 0.2 mol% MnO, attributed to electron emission from vacancy traps of V O •• and V O • , respectively. Increasing Mn content suppresses the low‐temperature relaxation and reduces low‐frequency dielectric loss (tanδ at 20 Hz from 1.80 to 0.68), while the intrinsic high‐frequency permittivity remains almost unchanged (ε′ ≈ 24, tanδ ≈ 0.06 at 1 MHz). The results are explained by a grain‐boundary space‐charge model with a vacancy‐rich, positively charged boundary core and Mn Zr ″‐enriched space‐charge layers, providing guidelines for tailoring CaZrO 3 ‐based dielectrics for base‐metal electrode applications.