The powders were prepared by a Pech

The powders were prepared by a Pechini‐type sol‐gel method.21 The chemicals, Zn(NO3)2.6H2O, Fe(NO3)3.9H2O,C6H8O7, and (CH2OH)2, were obtained from Loba Chemie, Mumbai, India, were used for the synthesis of the powders. Deionized water (DI water) with 0.1  μS/cm conductivity was used as the solvent. The chemicals with 150 H2O: 2Fe(NO3)3.9H2O: Zn(NO3)2.6H2O: 14 (CH2OH)2: n C6H8O7 (n = 2 and 4) molar ratios were dissolved in DI water. The obtained solution was stirred at 70°C until a viscous gel was obtained. The gel was dried at 200°C for 24 hours. The dried gel was milled with a planetary ball milling system (Fritsch, Germany) with yttria‐stabilized zirconia balls and cups for 30  minutes with a 5:1 ball‐to‐powder mass ratio. The obtained powder was calcined at 750°C for six hours within a box electrical furnace with a 10°C/min heating rate. 30 g of the powder was ground by a mortar‐pestle and was added to 50 mL of the 12 M solution of acetic acid in ethanol and stirred for 24 hours. Then, the suspension was filtered and the chemically treated powder was dried at room temperature. The chemically treated powder was mixed by adding 18‐21  wt% of the solution of acetic acid in ethanol. We emphasize that the amount of the solution for mixing with powder is a key parameter. Deviation from this range leads to failure of the CSP. The powder was placed in a steel die with a 2 cm diameter surrounded by a jacket heating element equipped with a temperature controller system. The powder was cold‐sintered by applying 300 MPa uniaxial pressure by heating the die to 280, 300, 320, and 350°C with 5°C/min heating rate. Th samples were removed from the die and dried at 200°C overnight. Then, the samples were postannealed at 750°C for 6 hours. Figure 1 schematically presents different stages of the CSP.