Crystal Structure and Electrical Properties of Ruthenium-Substituted Calcium Copper Titanate

This paper reports a detailed study of crystal structure and dielectric properties of ruthenium-substituted calcium-copper titanates (CaCu₃Ti_4-RuO₁₂, CCTRO). A series of three samples with different stoichiometry was prepared: CaCu₃Ti_4-RuO₁₂, x = 0, 1 and 4, abbreviated as CCTO, CCT3RO and CCRO, respectively. A detailed structural analysis of CCTRO samples was done by the Rietveld refinement of XRPD data. The results show that, regardless of whether Ti⁴⁺ or Ru⁴⁺ ions are placed in B crystallographic position in AA'₃B₄O₁₂ (CaCu₃Ti_4-RuO₁₂) unit cell, the crystal structure remains cubic with Im3¯ symmetry. Slight increases in the unit cell parameters, cell volume and interatomic distances indicate that Ru⁴⁺ ions with larger ionic radii (0.62 Å) than Ti⁴⁺ (0.605 Å) are incorporated in the CaCu₃Ti_4-RuO₁₂ crystal lattice. The structural investigations were confirmed using TEM, HRTEM and ADF/STEM analyses, including EDXS elemental mapping. The effect of Ru atoms share in CaCu₃Ti_4-RuO₁₂ samples on their electrical properties was determined by impedance and dielectric measurements. Results of dielectric measurements indicate that one atom of ruthenium per CaCu₃Ti₄RuO₁₂ unit cell transforms dielectric CCTO into conductive CCT3RO while preserving cubic crystal structure. Our findings about CCTO and CCT3RO ceramics promote them as ideal tandem to overcome the problem of stress on dielectric-electrode interfaces in capacitors.