Microstructure evolution and densification behavior of ultrafast high-temperature sintered Li_6.5La₃Zr_1.5Ta_0.5O₁₂ ceramics

Increasing the heating rate during the sintering process of Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) solid-state electrolyte is an effective method for suppressing lithium volatilization, tailoring grain growth, and achieving rapid densification. However, the ultrafast heating rate can lead to uneven surface temperature distribution of the electrolyte, subsequently affecting its microstructure and performance. Herein, we systematically investigate the microstructural evolution and densification behavior of LLZTO ceramics under rapid heating conditions using the ultrafast high-temperature sintering (UHS) method. An intercalibration technique combining finite element simulations and experimental data from infrared spectral measurements is used for prediction of the temperature distribution of the sample. Adjustment of the size ratio of the graphite felt to the sample diameter resulted in uniform temperature distribution, which aids in improving sintering quality. The densification mechanism of the samples during the UHS process is revealed by thermodynamics. Under sintering conditions with a current of 25 A applied for 30 s, the ultrafast heating rate (up to 10⁴ °C/min) results in fine grains with a diameter of approximately 3.4 μm and a relative density of 93.2 %. The preferred samples finally exhibit good ionic conductivity stability, maintaining 3.09 × 10⁻⁴ S cm⁻¹ at dynamic pressures of 5–50 MPa at room temperature.