To investigate the promotion of the

To investigate the promotion of the liquid phase during CSP on a more subtle level, TEM photographs of the ZrW2O8 samples with the liquid phase content of 10 wt% and 30 wt% are given in Fig. 4, respectively. Compared Fig. 4b with Fig. 4a, it’s clear the microstructure density of the sample with the liquid phase content 30 wt% is higher than that of the sample with only liquid phase content 10 wt%, since the glass phase (transformed by the residual liquid phase and the corresponding selected area electron diffraction is shown in Supplementary Information Fig. S2) in the sample plays a role as the ‘glue’ that bonding the adjacent particles. Pores are kept in Fig. 4a due to the lack of the liquid phase, but the trace of the sintered particles still can be found as shown in the white dashed rectangle in Fig. 4a. On the contrary, plenty of liquid phase in Fig. 4b fills the pores and clads the grains to form the clear phase boundary (as outlined by the white dashed line in Fig. 4d). Some nanocrystallites with short-range ordered lattices (as marked by the orange ellipses) can be discovered near the grain in Fig. 4c and Fig. 4d, which is attributed to the local hydrothermal synthesis of the added liquid phase HS during CSP and has been demonstrated in our previous work [8]. We also find the particle orientation in Fig. 4b is almost homogeneous, while the particle orientation in Fig. 4a shows disordered, indicating that the particle orientation is determined by the liquid phase content. Therefore, the above result demonstrates that the liquid phase plays a role as the carrier for the particle sliding, rotation and rearrangement.