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Tham khảo tài liệu 'ferroelectrics physical effects part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 150 Ferroelectrics - Physical Effects The crack length increased with increasing hydrogen concentration in the samples. Therefore the cracks can also grow with the prolongation of dwell time during indentation test in a precharged sample since the hydrogen concentration will increase at the indentation crack tips by stress-induced diffusion. The experimental results indicate that the longer the indentation load hold the larger the indentation crack length is and the smaller fracture toughness Kic H t measures as shown in Figure 14 Zhang et al. 2008 . Under a constant load the HIDC can occur by the stress-induced hydrogen diffusion and enrichment. Fig. 14. The normalized fracture toughness Kic H t Kịc versus the logarithm of the dwell time during the indentation test for the charged sample Zhang et al. 2008 5.3 Hydrogen-induced delayed cracking in ferroelectric ceramics During single-edge-notched-tensile sample of PZT ferroelectric ceramics hydrogen charging dynamically in 0.2mol l NaOH O.25 g 1 AS2O3 solution hydrogen-induced delayed cracking HIDC can occur Wang et al. 2003a and depends on the relative orientation between notch plane and the polarization vector i.e. the HIDC also shows anisotropy in ferroelectric ceramics as shown in Figure 15 Wang et al. 2003b . Hydrogen concentration Ch under different charging current densities is given in Table 2. The curve of Kih Kịc vs i or Ch can plot based on Table 2 and one can find a linear relationship between Kih Kịc and the IiĩCh Wang et al. 2003b Kfc KỈH K c 0.4-0.151nCH 5 where superscript a and b denote polarization vector parallel and perpendicular to the crack plane respectively. K c 1.53 MPam1 2 and Kp. 1.12 MPam1 2 for PZT ferroelectric Hydrogen in Ferroelectrics 151 i mA cm2 0.05 0.5 5 50 300 CH ppm 0.92 2.61 4.8 7.16 9.84 Kjh MPami 2 0.54 0.34 0.28 0.13 0.01 Kjh MPami 2 0.36 0.26 0.17 0.08 - IH i IC 0.40 0.25 0.21 0.10 0.01 -KỈH -KÌc 0.40 0.28 0.19 0.09 - Table 2. The threshold stress intensity factors of HIDC