1：Experimental Design and Method Selection:

The study uses 125Te NMR and impedance spectroscopy to investigate the surface properties of Bi2Te3 nanoparticles mixed with Al2O3 nanoparticles. The rationale is to control the surface-to-volume ratio by mixing with insulating nanoparticles, enhancing surface effects.

2：Sample Selection and Data Sources:

Bi2Te3 nanoparticles were synthesized via hydrothermal treatment using BiCl3, tellurium powder, NaOH, ethylenediaminetetraacetic disodium salt, and NaBH

3：Al2O3 nanoparticles (~50 nm) were mixed with Bi2Te3 in methanol at molar ratios of

3 and 2:

4：List of Experimental Equipment and Materials:

Equipment includes a Quadtech 7600 impedance analyzer, a Bruker AVANCE II+ 400-MHz NMR system, and materials include BiCl3, tellurium powder, NaOH, ethylenediaminetetraacetic disodium salt, NaBH4, Al2O3 nanoparticles, methanol, distilled water, ethanol, acetone.

5：Experimental Procedures and Operational Workflow:

Synthesis involved hydrothermal treatment at 200°C for 24h, washing and drying, mixing with Al2O3 in methanol with stirring at 50°C until evaporation. Impedance measurements were done from

6：3 Hz to 2 MHz with 01-V ac bias. NMR measurements were performed at 3 MHz with a liquid Te(OH)6 reference, using spin echo signals with echo delay of 10 μs and magic-angle spinning at 10 kHz. Data Analysis Methods:

NMR lineshapes were fitted with components to analyze Knight shift. Impedance data were fitted using equivalent circuit analysis to separate surface and bulk resistivities.