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<p>The next-generation energy and electronic systems face a significant challenge to reach the multifunctional behavior of the lead-free perovskite oxides. The present work was based on the synthesis of Ba<sub>1-x</sub>Cu<sub>x</sub>TiO<sub>3</sub> (<i>x</i> = 0.00, 0.01, and 0.03) ceramics through a solid-state process in order to explain how defect chemistry caused by Cu, distortion of lattices, and microstructural change control coupled dielectric, piezoelectric, optical, and magnetic behavior. X-ray diffraction and Rietveld refinement have verified the remnants of a distorted or pseudo-tetragonal P4mm average structure (c/a &gt; 1), showing defect-stabilized structural evolution instead of a tetragonal-cubic phase transition. The FTIR spectroscopy indicates the softening of the lattice and vibrational contribution of the Cu–O, whereas UV–Vis indicates the systematic reduction of the band gap between 3.18 and 2.89&#xa0;eV, increasing the optical absorption and conductivity. XPS demonstrates defect-mediated chemical modification while maintaining lattice stability by confirming Cu<sup>2+</sup> incorporation and enhanced oxygen-vacancy-related defect states without Ti<sup>3+</sup> formation. Dielectric and electrical measurements indicate the presence of non-Debye relaxation behavior, whose behavior is dictated by Maxwell–Wagner interfacial polarization, and oxygen-vacancy-assisted hopping conduction, which is supported by impedance (Z'/Z''), electric modulus (M'/M''), and frequency-dependent conductivity(s). Despite the reduction in long-range ferroelectric coherence and permittivity by the incorporation of Cu, the dielectric loss is low and constant at high frequencies, which points to higher reliability of the dielectric. Magnetic measurements indicate the development of room-temperature superparamagnetic-like behavior in compositions containing Cu, and it is actually due to the localized defect-mediated magnetic entities as opposed to secondary phases. It is noteworthy that the piezoelectric response is maximum at a moderate level of Cu content, where d<sub>33</sub> keeps rising between 191 and 230 pC/N, as well as improving the voltage coefficient and electromechanical coupling as a result of defect-assisted domain-wall mobility and defect-dipole interactions. In general, this paper creates a structural-property framework that is unified based on defects in Cu-doped BaTiO<sub>3</sub>, which places it as an effective lead-free multifunctional material platform in the future of piezoelectric, optoelectronic, and magneto-responsive applications.</p>

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Defect-mediated multifunctional behavior in Cu-doped BaTiO3: tunable superparamagnetism-like response, piezoelectricity, and optical absorption for next-generation magnetoelectric devices

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • R. Rajalakshmi,
  • P. Elaiyaraja,
  • V. Rachagar,
  • S. Chandra

摘要

The next-generation energy and electronic systems face a significant challenge to reach the multifunctional behavior of the lead-free perovskite oxides. The present work was based on the synthesis of Ba1-xCuxTiO3 (x = 0.00, 0.01, and 0.03) ceramics through a solid-state process in order to explain how defect chemistry caused by Cu, distortion of lattices, and microstructural change control coupled dielectric, piezoelectric, optical, and magnetic behavior. X-ray diffraction and Rietveld refinement have verified the remnants of a distorted or pseudo-tetragonal P4mm average structure (c/a > 1), showing defect-stabilized structural evolution instead of a tetragonal-cubic phase transition. The FTIR spectroscopy indicates the softening of the lattice and vibrational contribution of the Cu–O, whereas UV–Vis indicates the systematic reduction of the band gap between 3.18 and 2.89 eV, increasing the optical absorption and conductivity. XPS demonstrates defect-mediated chemical modification while maintaining lattice stability by confirming Cu2+ incorporation and enhanced oxygen-vacancy-related defect states without Ti3+ formation. Dielectric and electrical measurements indicate the presence of non-Debye relaxation behavior, whose behavior is dictated by Maxwell–Wagner interfacial polarization, and oxygen-vacancy-assisted hopping conduction, which is supported by impedance (Z'/Z''), electric modulus (M'/M''), and frequency-dependent conductivity(s). Despite the reduction in long-range ferroelectric coherence and permittivity by the incorporation of Cu, the dielectric loss is low and constant at high frequencies, which points to higher reliability of the dielectric. Magnetic measurements indicate the development of room-temperature superparamagnetic-like behavior in compositions containing Cu, and it is actually due to the localized defect-mediated magnetic entities as opposed to secondary phases. It is noteworthy that the piezoelectric response is maximum at a moderate level of Cu content, where d33 keeps rising between 191 and 230 pC/N, as well as improving the voltage coefficient and electromechanical coupling as a result of defect-assisted domain-wall mobility and defect-dipole interactions. In general, this paper creates a structural-property framework that is unified based on defects in Cu-doped BaTiO3, which places it as an effective lead-free multifunctional material platform in the future of piezoelectric, optoelectronic, and magneto-responsive applications.