Thermal Evolution and Optoelectronic Properties of KH 2 PO 4 ‐Modified Copper–Phosphoric Acid‐Based Geopolymers: A Multifunctional Glass‐Ceramic

Herein, we synthesized acid‐based‐geopolymer by blending metakaolin, KH 2 PO 4 and CuO with a diluted phosphoric acid. Structural changes during thermal treatments, were analyzed by X‐ray diffraction (XRD), thermogravimetric analysis‐derivative thermogravimetric (TGA‐DTG) and Raman spectroscopy. Accordingly, the geopolymer at room temperature, contained CuHPO 4 ·H 2 O crystals embedded in an amorphous phase. Raman analysis revealed AlPO 4 , and various bonds: Si─O─Al, Si─O─P, P─O─P, Si─O(H/Cu), P─O(H/Cu), O═P, structural units and , as well as a range of hydrated silica networks. EDS results confirmed the sample’s elemental composition. Heating the sample (400–600 °C) converts CuHPO 4 .H 2 O into Cu 2 P 2 O 7 , while the amorphous phase’s structural arrangement remains consistent with its room temperature form. After 800 °C calcination, the sample contains berlinite–AlPO 4 and quartz–SiO 2 nanodomains. Heating to 900 °C yields Cu 3 (PO 4 ) 2 crystals embedded in an amorphous AlPO 4 –SiO 2 matrix. At 1000 °C, a glass‐ceramic forms, dominated by an AlPO 4 –SiO 2 solid solution with cristobalite‐like structure. Morphologically, TGA and structural analysis support phase transformations subsequent to calcination. In addition, UV–vis reveals a temperature‐dependent bandgap redshift.