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<p>Lead-free ferroelectric ceramics based on sodium bismuth titanate (Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub>, NBT) are promising candidates for environmentally benign multifunctional devices; however, their practical application is limited by high coercive fields and restricted electromechanical response. In this study, 0.94Na<sub>0.5</sub>Bi<sub>0.5-<i>x-y</i></sub>Er<sub><i>x</i></sub>Yb<sub><i>y</i></sub>TiO<sub>3</sub>–0.06BaTiO<sub>3</sub> (NBEY-BT) ceramics with (<i>x</i> = <i>y</i> = 0.0 &amp; 0.1) were synthesized via a conventional solid-state route to investigate the effect of Er<sup>3+</sup>/Yb<sup>3+</sup> co-doping on the structural, microstructural, ferroelectric, and optical properties. X-ray diffraction combined with Rietveld refinement confirms a single-phase perovskite structure with coexisting rhombohedral (R3c) and tetragonal (P4mm) phases, characteristic of morphotropic phase boundary behavior. Er<sup>3+</sup>/Yb<sup>3+</sup> co-substitution increases the tetragonal phase fraction and induces local lattice strain without forming secondary phases. Microstructural analysis reveals dense ceramics with uniform grain distribution and a reduced average grain size upon rare-earth doping. Ferroelectric measurements show well-saturated polarization–electric field hysteresis loops, with the co-doped composition exhibiting a reduced coercive field and enhanced domain switchability while maintaining high polarization. A pronounced improvement in piezoelectric performance is achieved in the doped composition, which exhibits higher d₃₃ values at lower electric fields due to facilitated non-180° domain switching and polarization rotation near the morphotropic phase boundary. Furthermore, efficient Yb<sup>3+</sup>-sensitized Er<sup>3+</sup> upconversion photoluminescence under 980&#xa0;nm excitation is observed, introducing multifunctional optical functionality absent in the undoped ceramic. Notably, only the Er<sup>3+</sup>/Yb<sup>3+</sup>-substituted ceramics display strong upconversion photoluminescence under 980&#xa0;nm excitation, characterized by green (<sup>4</sup>S<sub>3/2</sub> → <sup>4</sup>I<sub>15/2</sub>) and red (<sup>4</sup>F<sub>9/2</sub> → <sup>4</sup>I<sub>15/2</sub>) emissions arising from efficient Yb<sup>3+</sup> → Er<sup>3+</sup> energy transfer. The coexistence of ferroelectric polarization and upconversion luminescence in NBEY-BT ceramics highlights their potential as multifunctional dipolar luminescent materials for advanced optoelectronic, sensing, and energy-harvesting applications.</p>

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Morphotropic phase boundary modulation via Er3+/Yb3+ Co-substitution in lead-free NBT–BT ceramics for multifunctional dielectric, piezoelectric, and optical applications

  • 期刊论文

  • 发表日期：

    2026年4月29日

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  • N. Manohar Reddy,
  • P. Sreenivasa Rao,
  • Ch. Rajasekhar,
  • T. Radha Rani,
  • P. H. K. Charan,
  • Ramu Boddepalli,
  • Manjula Bharathi Nagulapati,
  • C. Jayakumar,
  • Kavuluri Pushpalatha,
  • Nageswara Rao Medikondu,
  • M. Ramanaiah

摘要

Lead-free ferroelectric ceramics based on sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) are promising candidates for environmentally benign multifunctional devices; however, their practical application is limited by high coercive fields and restricted electromechanical response. In this study, 0.94Na0.5Bi0.5-x-yErxYbyTiO3–0.06BaTiO3 (NBEY-BT) ceramics with (x = y = 0.0 & 0.1) were synthesized via a conventional solid-state route to investigate the effect of Er3+/Yb3+ co-doping on the structural, microstructural, ferroelectric, and optical properties. X-ray diffraction combined with Rietveld refinement confirms a single-phase perovskite structure with coexisting rhombohedral (R3c) and tetragonal (P4mm) phases, characteristic of morphotropic phase boundary behavior. Er3+/Yb3+ co-substitution increases the tetragonal phase fraction and induces local lattice strain without forming secondary phases. Microstructural analysis reveals dense ceramics with uniform grain distribution and a reduced average grain size upon rare-earth doping. Ferroelectric measurements show well-saturated polarization–electric field hysteresis loops, with the co-doped composition exhibiting a reduced coercive field and enhanced domain switchability while maintaining high polarization. A pronounced improvement in piezoelectric performance is achieved in the doped composition, which exhibits higher d₃₃ values at lower electric fields due to facilitated non-180° domain switching and polarization rotation near the morphotropic phase boundary. Furthermore, efficient Yb3+-sensitized Er3+ upconversion photoluminescence under 980 nm excitation is observed, introducing multifunctional optical functionality absent in the undoped ceramic. Notably, only the Er3+/Yb3+-substituted ceramics display strong upconversion photoluminescence under 980 nm excitation, characterized by green (4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) emissions arising from efficient Yb3+ → Er3+ energy transfer. The coexistence of ferroelectric polarization and upconversion luminescence in NBEY-BT ceramics highlights their potential as multifunctional dipolar luminescent materials for advanced optoelectronic, sensing, and energy-harvesting applications.