*2.3. Characterization*

The crystal phases of all samples were characterized by X-ray diffraction (XRD, Empyrean, PANalytical B.V., Amsterdem, Netherlands). RENISHAW Raman microscope (Raman, In Via, RENISHAW, England) was used to measure modified salts and magnesium oxide nanoparticles. We observed the microstructure of the sample with a field emission scanning electron microscope (SEM, S-4800, HITACHI, Tokyo, Japan). The component analysis of the prepared modified nitrate was examined by X-ray energy-dispersive spectroscopy (EDS, AMETEK, Berwyn, PA, USA) combined with scanning electron microscopy under a constant nitrogen flow from 30 to 200 ◦C at a heating rate of 10 ◦C/min. The specific heat capacity and latent heat of phase change of the samples were measured with a differential scanning calorimeter (DSC8500, PERKINELMER, Waltham, MA, USA). Then, we used an infrared thermal imager (TESTO-872, Testo SE&Co. KGaA, Titisee-Neustadt, Germany) to characterize the heat transfer performance of ternary nitrate modified with different percentages of MgO nanoparticles. Thermal diffusivity was obtained by a laser thermal conductivity meter (LFA457, NETZSCH, Selb, Germany).
