Crystal structure and phase formation of MgO-MoO₃-based ceramics with ultralow dielectric loss: A comprehensive study

The MgO-MoO3 system shows significant potential for applications in microwave dielectric ceramics. However, the formation mechanism, crystal structures, and microwave dielectric properties of this system have not been systematically investigated. This work aims to comprehensively study the crystal structures, phase transitions, and microwave dielectric properties of compounds in the MgO-MoO3 system. In particular, the research delves into the unexplored transformation mechanism from beta-MgMo2O7 to alpha-MgMo2O7 and MgMoO4. As a result, the three compounds exhibiting favorable microwave dielectric properties have been successfully fabricated. These compounds can be effectively sintered at temperatures ranging from 685 to 900 degrees C and exhibited dielectric constants (epsilon(r)) ranging from 5.41 to 6.89, as well as Qf values ranging from 100 000 to 130 000 GHz. Additionally, prototype microstrip antennas are designed and fabricated using beta-MgMo2O7 and MgMoO4 ceramics as substrates. The obtained antenna's performance is excellent, with S-11 values below -30 dB and a gain exceeding 6 dB at 5.8 GHz, highlighting the potential of the developed ceramics for practical applications in microwave devices.