“…In addition, the ionic radius of Ti 4+ , Zn 2+ , and Ta 5+ are around 0.605 Å, 0.74 Å, and 0.64 Å, respectively. The small mismatch of ionic radius between Ta 5+ , Zn 2+ , and Ti 4+ indicates impurity phase is hard to formed, which is different from rare earth codoped TiO 2 ceramics [16,17,20,30]. The Figure 1(b) clearly shows that the (110) diffraction peak slightly shifts toward a lower angle, which indicates that Ta and Zn on the Ti site leads to a larger cell volume due to lattice expansion.…”