Interplay of pH and combustion stoichiometry governing microstructure, magnetism, and microwave absorption in Li0.5Cr0.5Fe2O4 ferrites

The controlled variation of combustion conditions profoundly alters the crystallization pathway, grain growth, and defect chemistry. To establish their combined influence on structural, morphological, magnetic, and microwave absorption behavior lithium chromium (Li–Cr) ferrite (Li 0 . 5 Cr 0 . 5 Fe 2 O 4 ) were systematically synthesized through a sol-gel auto-combustion route by simultaneously tuning the nitrate-to-fuel molar ratio (1:2, 1:2.22, 1:3) and pH (1, 3, 5, 7, 9). Thermogravimetric analysis with differential scanning calorimetry (TGA/DSC) results revealed enhanced thermal stability and more complete phase evolution at neutral and mildly basic conditions, whereas acidic media induced incomplete combustion and amorphous intermediates. Rietveld refined XRD confirmed the formation of a cubic spinel phase in all samples, with lattice parameters and crystallite sizes strongly dependent on pH-fuel synergy. Sharper diffraction peaks, enhanced crystallinity, and optimal lattice homogeneity were encouraged by higher pH (5-9) and stoichiometric fuel conditions. The distinctive metal-oxygen vibrations and local structural distortions caused by Cr substitution were confirmed by FTIR and Raman spectra. Morphological research revealed variations in porosity and grain aggregation patterns caused by pH. Superior saturation magnetization, dielectric response, and microwave absorption in the X-band (8-12 GHz) frequency region are shown by samples synthesized near stoichiometric fuel ratio and mild pH, according to magnetic and VNA measurements. These results give a tunable approach to optimize Li–Cr ferrites for next-generation electromagnetic shielding and absorption devices, as well as fresh insight into sol-gel auto-combustion chemistry.