## 3 Results and Discussion
### Results of Characterization of Materials
#### 3.1.1 Platinum-Based Powder and Sintered Material
Figure 3C presents the measured and calculated patterns of the prepared mixture and the crystalline phases employed in the refinement. The refinement procedure resulted in 14.5 wt. % of the metallic platinum phase and 85.5 wt. % of ZnO in the overall mass of the crystalline phases contained in the mixture of the two powders. Therefore, the content of the metallic platinum phase in the platinum-based powder could be calculated as (14.5/85.5)\(\cdot\)100%, thus yielding about 17.0 wt. %. The remaining 83.0 wt. % was accounted for as the amorphous phase (PtO, according to XPS data). The obtained data correlate well with those reported in [26]: 14.4 wt. % of metallic platinum and 85.6 wt. % of the amorphous phase (PtO, with x = 1.12, as the authors estimated from EDX analysis). It follows from the TEM images (Figure 4A-C) that the powder was composed of nearly spherical particles, particles of irregular shapes and faceted particles. Some of them exhibited distinct core-shell structures (Figure 4C,D). The selected area electron diffraction (SAED) pattern presented in the inset of Figure 4A consists of rings corresponding to interplanar spacings of 2.25, 1.94, 1.36 and 1.17 A. These values are in good agreement with those characteristic of (111), (200), (220), and (311) planes of platinum with Fm3m crystal structures. Therefore, the results obtained from the SAED and XRD studies were consistent. Furthermore, taking into account the results of the XPS and XRD examinations, one may conclude that a certain fraction of the powder was represented by amorphous platinum oxide particles, while the other one was represented by particles possessing core-shell structures with a crystalline platinum core and an amorphous platinum oxide shell. Figure 5A demonstrates a histogram representing the size distribution of a number fraction of individual particles, fitted by a log-normal distribution. The calculated, normalized number-weighted and volume-weighted probability density functions are presented in Figure 5B. Figure 3: X-ray diffraction (XRD) spectra of the platinum-based powder (**A**), sintered material (**B**) and mixture (1:1 by weight) of the platinum-based powder with ZnO powder, used as a crystalline internal standard (**C**). The spectra were acquired by using Cu K\(\alpha\) radiation. The lines corresponding to Al\({}_{2}\)O\({}_{3}\) observed in the spectrum of the sintered material are due to the contribution of alumina substrate, used for the deposition of the formulated ink. Figure 6 presents the SEM image of the sintered line, printed on alumina substrate, together with the EDX elemental mappings. A typical EDX spectrum of the sintered  
Figure 4: Transmission electron microscopy (TEM) images of nanoparticles at different magnifications (**A**–**D**) and the electron diffraction pattern (inset of **(A)**). Figure 5: Histogram representing the size distribution of a number fraction of individual particles fitted by a log-normal distribution (**A**) and the normalized number-weighted \(\mathrm{P_{N}(D)}\) and volume-weighted \(\mathrm{P_{V}(D)}\) probability density functions (**B**). material is shown in Figure 7. Figure 8 presents the SEM images of the sintered material at higher magnifications. It follows from these images that the obtained material was characterized by a high degree of sintering. The size of most crystallites was in the range between 100 and 400 nm. The resistivity of the sintered material, calculated based on the results of the measurements of 10 printed lines, was found to be (1.2 \(\pm\) 0.1)\(\cdot\)10\({}^{-7}\)\(\Omega\cdot\)m at 25 \({}^{\circ}\)C, thus exceeding that of bulk platinum by a factor of about 1.1. Since the content of platinum in the sintered material was 99.7 wt. % and the oxidation state of the platinum therein was zero, as evidenced by the ICP-AES and XPS data, the observed difference in the resistivity was due to the insignificant residual porosity of the sintered material (Figure 8).