The impact of microstructural heterogeneities on hotspot formation in flash sintering: Li₃V₂(PO₄)₃ as a case study

Flash sintering (FS) enables rapid, energy-efficient ceramic densification at reduced temperatures but suffers from hot spot formation that compromises microstructural homogeneity and mechanical integrity. This study investigates hot spot development during FS of Li 3 V 2 (PO 4 ) 3 (LVP), a mixed ionic-electronic conductor of interest for all-solid-state battery positive electrode material. Experiments conducted at 300 °C and 100 V/cm demonstrated successful flash events but revealed hot spot formation at current densities ≥ 4 A/cm², causing localized densification and sample fracturing. By combining interrupted FS experiments with X-ray microtomography, we revealed a correlation between microstructural heterogeneities in green pellets and the formation of hot spots during sintering. Our quantitative analysis, based on X-ray tomography data, demonstrated that even minor local density fluctuations (as low as 2%) drastically influence current percolation pathways and trigger thermal runaway events. These findings underscore the critical importance of achieving homogeneous green bodies to prevent localized overheating and ensure uniform densification. • Successful densification of Li₃V₂(PO₄)₃ (LVP) at just 300°C under a moderate electric field (100 V/cm), achieving high-phase-purity densified regions. • Critical hot spot mechanisms: Identification of a 4 A/cm² threshold, beyond which hot spot formation becomes inevitable, leading to sample fracturing and non-uniform densification. • Microstructure-hot spot correlation: X-ray microtomography reveals a direct link between minor initial density variations (≥ 2%) in green pellets and hot spot development during flash sintering. • Role of initial homogeneity: Emphasizes the critical importance of powder processing and green body preparation, which are as decisive as sintering parameters in preventing defects.