Tailoring Phase Transition and Dielectric Response in BaTiO₃ Ceramics via Sb₂O₃ Doping

Ferroelectric ceramics are extensively utilized in advanced fields such as pyroelectric sensors, energy storage devices, and electrocaloric refrigeration systems. These applications are highly reliant on their phase transition behavior and dielectric properties. For instance, remarkable pyroelectric and electrocaloric effects are typically achieved near the Curie temperature (T_C), where the ferroelectric-to-paraelectric phase transition occurs [1]. Similarly, superior energy storage performance, characterized by low energy loss, requires excellent relaxor ferroelectric characteristics [2].

Barium titanate (BaTiO₃) is a classic lead-free ferroelectric material that undergoes a sharp first-order ferroelectric-toparaelectric phase transition around T_C ≈ 125°C [3]. This inherent feature severely restricts its room-temperature pyroelectric, electrocaloric performances, and energy storage capability. To broaden its application scope, cation substitution is the most conventional and effective strategy for tailoring the phase transition and dielectric response. Typical routes include replacing Ba²⁺ with Ca²⁺, Sr²⁺, or rare-earth ions (RE³⁺, where RE = La, Ce, Nd, Sm, Eu, Gd, Dy, Er) and substituting Ti⁴⁺ with Zr⁴⁺, Sn⁴⁺, or Hf⁴⁺ [4].

Different from the conventional cation substitution strategy, this work proposes directly introducing the metal oxide Sb₂O₃ into BaTiO₃ ceramics to tailor its phase transition and dielectric response. This novel modification approach is expected to optimize its pyroelectric, electrocaloric, and energy storage performances, thereby further expanding its application scope.

BaTiO₃+xSb₂O₃ ceramics (x = 0, 0.01, 0.02, 0.03) were prepared by a conventional solid-state reaction method, using BaCO₃, TiO₂, Sb₂O₃. The homogenized mixed powders were calcinated at 1150°C for 3 h, followed by sintering at 1350°C for 2 h to obtain bulk ceramics. The phase structures were characterized by an X-ray diffractometer (XRD, Shimadzu LabX, Japan). A differential scanning calorimeter (DSC, TA Q2000, USA) was employed to collect heat flow data. Dielectric properties were measured by precision impedance analyzer (Wayne Kerr WK6500P, UK) coupled with a temperature-control and data-collect system (BALAB DMS- 2000, China).

Figure 1 presents the XRD patterns of BaTiO₃+xSb₂O₃ ceramics. All samples exhibit a pure perovskite structure without detectable secondary phases, indicating that Sb₂O₃ has been fully incorporated into the BaTiO₃ lattice. Undoped BaTiO3 displays a distinct (002)/ (200) peak splitting at 2θ ≈ 45°, which is consistent with tetragonal (T) P4mm symmetry [5]. In contrast, a single diffraction peak is obtained near 2θ ≈ 45° for doped BaTiO₃, manifesting a pseudocubic structure. This result demonstrates that the introduction of Sb₂O₃ disturbs the long-range ordered lattice structure of BaTiO₃.

Figure 2 presents the heat flow curves of BaTiOsub>3+xSb₂O₃ ceramics measured in the temperature range of -50°C to 150°C during heating. For pure BaTiOsub>3, two sharp endothermal peaks are observed, among which, the low-temperature peak near 19°C corresponds to orthorhombic-tetragonal (O-T) first-order ferroelectric phase transition, while the high-temperature peak at 125°C, i.e T_C, arises from the tetragonal-cubic (T-C) first-order ferroelectric-to-paraelectric phase transition [6]. When Sb₂O₃ is doped at x=0.01, both endothermal peaks weaken significantly, and TC shifts to a lower temperature (75°C). With further increasing Sb₂O₃ doping content, the endothermal peaks gradually diminish. This indicates that Sb₂O₃ doping facilitates the transformation of the phase transition from a first-order to a diffuse type.

Figure 3 illustrates the temperature dependences of dielectric constants (εr) and losses of BaTiO₃+xSb₂O₃ ceramics at frequencies ranging from 0.1 to 1000 kHz. Consistent with the heat flow results, pure BaTiO₃ exhibits first-order phase transitions around 19°C (OT) and 125°C (T-C). Additionally, an extra dielectric peak is observed at -75°C, corresponding to the rhombohedral-orthorhombic (R-O) phase transition [6]. For the x=0.01 doped sample, the T_C shifts to 77°C, and the dielectric peaks corresponding to the R-O and O-T phase transitions become flattened. Notably, x=0.02 and x=0.03 samples only show a single dielectric peak corresponding to T_C at 38°C and 22°C, respectively, which is conducive to their roomtemperature applications.

To further quantify the phase transition diffuseness, the modified Curie–Weiss law was employed [7]. Figure 4 displays the plots and linear fittings of ln(1/ε_r-1/ε_m) and ln(T-T_m) at 1000 kHz, where ε_m is the maximum dielectric constant and T_m is the temperature corresponding to ε_m. All sample data can be well fitted linearly, and the slope of the fitting line is defined as the diffusion factor (γ). With the increase of Sb₂O₃ doping content from x = 0 to x = 0.03, the diffusive factor increases from γ = 1.05 to γ = 1.99. A γ value close to 1 indicates a normal ferroelectric, while a γ value approaching 2 is characteristic of a relaxor ferroelectric. This result further confirms that Sb₂O₃ doping converts the phase transition of BaTiO₃ from a first-order to a diffuse type.

This work achieves BaTiO₃ modification via direct Sb₂O₃ introduction. The results show that Sb₂O₃ can be fully dissolved into the BaTiO₃ lattice to form a pure perovskite phase, triggering a structural transformation from tetragonal to pseudo-cubic symmetry. Meanwhile, it converts original first-order phase transition of BaTiO₃ to a diffuse type, endowing the material with relaxor ferroelectric properties, and shifts the Curie temperature toward room temperature. This novel modification strategy provides effective support for optimizing the performances of BaTiO₃ and expanding its application prospects.

This work was supported by the National Undergraduate Innovation and Entrepreneurship Training Program (No. 202410621019).

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