Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO₄...

Area of Science:

• Materials Science
• Solid State Chemistry
• Dielectric Ceramics

Background:

• Microwave dielectric ceramics with permittivity (~20) are vital for 5G massive MIMO technology.
• Fergusonite-structured materials offer low dielectric loss but face challenges in tuning the temperature coefficient of resonant frequency (TCF).
• Nd(Nb)O4 ceramics are promising but require TCF optimization for practical applications.

Purpose of the Study:

• To tune the temperature coefficient of resonant frequency (TCF) in Nd(Nb)O4 ceramics for 5G applications.
• To investigate the effect of Vanadium (V5+) substitution for Niobium (Nb5+) on the phase transition and dielectric properties.
• To demonstrate a method for designing near-zero TCF compositions in fergusonite systems.

Main Methods:

• Substitution of smaller V5+ ions for Nb5+ in Nd(Nb1-xVx)O4 ceramics.
• In situ X-ray diffraction to determine the fergusonite-to-scheelite phase transition temperature (TF-S).
• Measurement of thermal expansion coefficient (αL) and dielectric properties (permittivity ε, quality factor Qf, temperature coefficient of permittivity τ_ε).

Main Results:

• V5+ substitution lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x=0.2.
• The thermal expansion coefficients of the scheelite and fergusonite phases were determined (+11 ppm/°C and +14 to +15 ppm/°C, respectively).
• Nd(Nb0.8V0.2)O4 exhibited a near-zero TCF of +7.8 ppm/°C, with permittivity ε ~ 18.6 and Qf ~ 70,100 GHz, due to modulated τ_ε and αL at TF-S.

Conclusions:

• A method to achieve near-zero TCF in Nd(Nb)O4 ceramics was successfully demonstrated by modulating τ_ε and αL at the phase transition temperature.
• The substitution strategy provides a pathway for designing advanced microwave dielectric materials for 5G and beyond.
• This approach is potentially extendable to other fergusonite-based ceramic systems.