Glass-free MgO-based microwave dielectric ceramics (1-x) wt% (0.98 MgO-0.02 Al₂O₃)-x wt% LiF (x = 0.5, 1, 2, 3, 4) were synthesized where LiF and Al₂O₃ were utilized as sintering additive and reinforcement phase in MgO matrix respectively. It was found that ion substitution is apt to occur between LiF and MgO, leading to the formation of oxygen vacancies and MgF₂. Nevertheless, different from ordinary liquid-phase sintering, morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering. Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties. Moreover, LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics, which is dominated by electrical breakdown mechanism. Combination of good properties were achieved in 1 wt% LiF modified MgO-based ceramics sintered at 950 °C which exhibited superior microwave properties (ε_r = 9.56, tanδ = 9.2 × 10⁻⁵, Qf = 124,600 GHz), high flexural strength (184.5 MPa), high thermal conductivity (21.3 W/(m⋅K)), high coefficient of thermal expansion (∼12 ppm/°C) and moderate electrical properties (E_b = 35.9 kV/mm, ρ = 4.9 × 10¹² Ω cm).

合成了无玻璃的基于MgO的微波介电陶瓷（1-x）wt％（0.98 MgO-0.02 Al ₂ O ₃）-x wt％LiF（x = 0.5、1、2、3、4），其中LiF和Al ₂ O ₃分别用作MgO基体的烧结添加剂和增强相。发现在LiF和MgO之间易于发生离子取代，从而导致氧空位和MgF ₂的形成。。然而，与普通液相烧结不同，当引入过量的LiF时，陶瓷的形貌会发生明显的变化，晶粒从多面体变为球形，并且密度显着降低，我们称之为过量液相烧结。这种情况引起的晶界弱化将对物理性能产生不利影响。此外，添加LiF大大降低了介电击穿强度，并改变了以电击穿机理为主导的MgO基陶瓷的介电击穿行为。在950°C下烧结的1 wt％LiF改性的MgO基陶瓷实现了良好的性能组合，这些陶瓷表现出优异的微波性能（_εr  = 9.56，tanδ= 9.2×10 ^-5Qf = 124,600 GHz），高抗弯强度（184.5 MPa），高导热率（21.3 W /（m·K）），高热膨胀系数（〜12 ppm /°C）和适度的电性能（E _b  = 35.9千伏/毫米，ρ= 4.9×10 ¹²  Ω厘米）。