1：Experimental Design and Method Selection:

The study used a hydrothermal method to synthesize Cr-doped BiPO4 pigments with varying Cr3+ concentrations. Characterization techniques included XRD, FTIR, FE-SEM, HR-TEM, XPS, UV-Vis-NIR spectroscopy, colorimetry, TG-DTA, and corrosion resistance tests. Application studies involved dispersing pigments in PMMA and testing reflectance, surface temperature, and heat aging.

2：Sample Selection and Data Sources:

Pigments were synthesized with formula Bi1-xCrxPO4 (x = 0.00 to 0.40). PMMA was used as the polymer matrix. Data were obtained from laboratory experiments and standard references.

3：00 to 40). PMMA was used as the polymer matrix. Data were obtained from laboratory experiments and standard references. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included XRD (Bruker D8 ADVANCE), FTIR (Thermo Fisher Nicolet iS10), FE-SEM (Hitachi S-4800II), HR-TEM (FEI Tecnai G2 F30 S-Twin), XPS (Thermo Fisher ESCALAB250Xi), UV-Vis-NIR spectrophotometer (PerkinElmer Lambda 950), colorimeter (Konica Minolta CM-2500d), TG-DTA (HENVEN HCT-4), infrared thermal camera (FLIR SC7000), and aging oven (MZHU401A). Materials included NaH2PO4·2H2O, Bi(NO3)3·5H2O, Cr(NO3)3·9H2O, glycerol, distilled water, ethanol, BaSO4, and PMMA.

4：Experimental Procedures and Operational Workflow:

Pigments were synthesized hydrothermally at 160°C for 24h, washed, dried, and characterized. For application, pigments were mixed with PMMA (10 wt%), compressed into sheets, and tested for reflectance, surface temperature, and heat aging at 110°C for 24h.

5：4h. Data Analysis Methods:

5. Data Analysis Methods: Data were analyzed using Jade6.0 software for XRD, Kubelka-Munk function for reflectance, CIE L*a*b* for color, and standard calculations for reflectance and color difference.