Lattice evolution, order transformation, and microwave dielectric properties of the Zn <sub>1− <i>x</i> </sub>Li <sub>2 <i>x</i> </sub>TiO <sub>3</sub> (0 ≤ <i>x</i> ≤ 1) system ceramics
Qianbiao Du, Longxiang Jiang, Linzhao Ma, Jianhong Duan, Zeyan Zhou, Hao Li
Abstract
Research on doping modification of ZnTiO<sub>3</sub> ceramics to enhance microwave dielectric properties has been hindered by poor performance, unclear structure-function mechanisms. To expand the applicability of ZnTiO<sub>3</sub> ceramics, this study explores Zn<sub>1–<i>x</i></sub>Li<sub>2<i>x</i></sub>TiO<sub>3</sub> (0 ≤ <i>x</i> ≤ 1) ceramics using a phase engineering strategy. Our findings reveal that the introduction of Li<sup>+</sup> into the ZnTiO<sub>3</sub> system initiates a multiple phase transition, starting at <i>x</i> = 0.1. Initially, ilmenite ZnTiO<sub>3</sub> transforms into a cubic ordered spinel phase (space group <i>P</i>4332). Subsequently, a transition to a disordered spinel phase (space group <i>Fd</i><inline-formula id="Z-2024081321305600000000000000000000"> <math id="mathml_Z-2024081321305600000000000000000000" display="inline" overflow="scroll"><mrow class="MJX-TeXAtom-ORD"><mover><mn>3</mn><mo stretchy="false">¯</mo></mover></mrow></math></inline-formula><i>m</i>) occurs at <i>x</i> = 0.5, culminating in the formation of a monoclinic rock salt-structured Li<sub>2</sub>TiO<sub>3</sub> phase. Significantly, two sets of ceramics with near-zero temperature coefficients of resonance frequency (<i>τ</i><sub>f</sub>) were obtained at <i>x</i> = 0.1 and 0.75. Moreover, the quality factor (<i>Q</i>×<i>f</i>) demonstrated a 4.4-fold increase compared to that of ZnTiO<sub>3</sub> ceramics at <i>x</i> = 0.25 (105,013 GHz). Additionally, it was observed that the Ti<sup>4+</sup> polarization in Zn<sub>1−<i>x</i></sub>Li<sub>2<i>x</i></sub>TiO<sub>3</sub> ceramics was underestimated by 11.3%–13.3%, causing the measured dielectric constant (<i>ε</i><sub>r</sub>) exceeding the theoretical dielectric constant (<i>ε</i><sub>th</sub>). The ionic polarizability of Ti<sup>4+</sup> was adjusted to stabilize around 3.29 Å<sup>3</sup>. Evaluation using multiple methods, including Phillips–van Vechten–Levine (P–V–L) theory, Raman vibrational mode analysis, bond valence, bond energy theory, and octahedral distortion, confirms that the Ti–O bonds within the octahedron predominantly affect <i>ε</i><sub>r</sub>, the increasing lattice energy (<i>U</i>) contributes to the enhancement of <i>Q</i>×<i>f</i>, and the strengthened Li–O bond energy effectively regulates <i>τ</i><sub>f</sub>.