## 2 Materials and Methods  
YSZ ceramics were prepared from commercial cubic yttrium-stabilized zirconia nanopowder (TZ-10 YS, TOSOH corp., Shunan, Japan). The SPS-515S installations (Syntex Inc., Kawasaki, Japan) at Tomsk Polytechnic University and Labox 1575 (Sinter Land Inc., Kawasaki Japan) at the Lavrentyev Institute of Hydrodynamics SB RAS were used for powder consolidation. The sintering process was carried out in a vacuum (10\({}^{-3}\) Pa) at a temperature of 1300 \({}^{\circ}\)C. Heating from room temperature to 1000 \({}^{\circ}\)C was carried out at a rate of 15 \({}^{\circ}\)C/min--from 1000 to 1300 \({}^{\circ}\)C at the rate 10 \({}^{\circ}\)C/min. The holding time at a given sintering temperature was 10 min. The pulse relative duration was 3:1. The temperature during sintering was controlled by a high-temperature pyrometer through a technological hole made on the side surface of the graphite die. Pressing in the SPS process was conducted using both the conventional uniaxial method and collector pressing. The prepressing pressure throughout the SPS process remained unchanged and amounted to 100 MPa. A detailed description of the selected sintering mode is presented in [12]. The collector pressing method was implemented by using split dies of various designs. The dies consisted of two solid or composite forming elements moving oppositely during the pressing process. They contained part of the active and part of the passive forming surfaces. The powder compaction occurred due to their mutual counter-movements when sliding along each other along the pressing axis [11]. Figure 1 shows a die with counter-moving parts of the passive forming surface (elements 4 and 4), designed by us to implement the collector pressing scheme in the SPS process. In order to gain statistically reliable data, 3 samples of each thickness were obtained for both pressing methods. Transparent cylindrical ceramic specimens with diameters of 14 mm and heights of 2.5 to 5.5 mm were obtained by the SPS technique. Further study of the ceramics was carried out after mechanical polishing of their end surfaces on an EcoMet 300 Pro grinding and polishing system (Buehler, Germany) using Kemix diamond suspensions (Kemika, Russia). The height (_h_) of the polished samples ranged from 2 to 5 mm, which corresponds to a shape factor (ratio of height to diameter) of 0.14 to 0.36. The YSZ ceramics were annealed in an atmospheric furnace LHT 02/18 (Nabertherm, Germany) in an air atmosphere at 800 \({}^{\circ}\)C for 4 h to achieve optimal stoichiometry with respect to oxygen and to reduce the concentration of defects associated with oxygen vacancies formed in the SPS process in a vacuum. The study of the rheological characteristics of the powder body consolidated by the SPS technique was carried out using the method of approximating the experimental compaction data by a dimensionless equation of a logarithmic form [13]:  
\[\rho=b\cdot\ln\left(\frac{P_{p}}{P_{c}}+\left[\frac{T_{p}}{T_{c}}\right]^{n} \right)+1 \tag{1}\]  
where \(\rho\) is the relative density of the powder body, \(b\) is the coefficient characterizing the intensity of compaction of the powder body under the action of the pressing pressure, \(P_{p}\) is the pressing pressure, \(P_{c}\) is the critical pressing pressure at which the nonporous state of the powder body is achieved, \(T_{p}/T_{c}\) is the relative temperature, and \(n\) is the power constant, which characterizes the rate of change of the relative density with increasing temperature. X-ray phase analysis of the initial YSZ powder and ceramics was characterized using an XRD-7000S X-ray diffractometer (Shimadzu, Japan) using Cu\(K_{\alpha}\) radiation (\(\lambda\) = 1.54,056 A). The interpretation of the results was conducted using the PDF-4 international crystallographic database and PowderCell 2.4 free software.