Phase composition, microstructure, and microwave dielectric properties of non-stoichiometric yttrium aluminum garnet ceramics

Lattice evolution and microwave dielectric properties of La‐doped yttrium aluminum garnet ceramics

“…In addition, the near-zero temperature coefficient (τ f ) reflects the device's operating stability. [3][4][5][6][7] In recent years, the research and application of garnetbased ceramics in the field of microwave dielectrics have been greatly promoted. On the one hand, breakthroughs have been made in the microwave dielectric properties of novel garnet-based ceramics, for example, Sr 2 NaMg 2 V 3 O 12 8 with ε r = 11.7, Q × f of 37,950 GHz, and τ f value of −2.9 ppm/ • C; Ca 3 B 2 GeV 2 O 12 (B = Mg, Mn) 9 with ε r of 9.75 and 11.06, Q × f of 54,000 and 30,240 GHz, τ f of −61.2 and −66.4 ppm/ • C; A 3 Y 2 Ge 3 O 12 (A = Ca, Mg) 10 with ε r = 10.8 and 14.1, Q × f = 97,126 and 12,600 GHz, and τ f = −40.6 and 120.5 ppm/ • C; Sr 3 B 2 Ge 3 O 12 (B = Yb, Ho) 11 with ε r = 9.30 and 9.23, Q × f = 129,360 and 104,600 GHz, τ f = −42 and −26 ppm/ • C; Ca 3 MgBGe 3 O 12 (B = Zr, Sn) 12 ceramics with ε r = 10.80 and 9.68; Q × f = 79,600 and 83,400 GHz; and τ f = −66.8 and −57.9 ± 1 ppm/ • C. On the other hand, research studies on the modification of conventional yttrium aluminum garnets have also exhibited achievements.…”

“…In 2016, Yu et al 13 reported the microwave dielectric properties of pure Y 3 Al 5 O 12 (YAG) transparent ceramics sintered at 1800 • C for 12 h: ε r = 10.8, Q × f = 213,400 GHz, and τ f = −30 ppm/ • C. In 2022, Wu et al 14 prepared Y 3 Mg 0.5 Al 4 Si 0.5 O 12 ceramics sintered at 1625 • C for 5 h by Mg 2+ and Si 4+ co-modifying and obtained excellent microwave dielectric properties with ε r = 10.56, Q × f = 67,571 GHz, and τ f = −35.23 ppm/ • C. However, due to the strict preparation process, the main research direction of ceramics in this system focuses on reducing the sintering temperature and improving the density of the ceramics, like adding sintering aid TEOS, 15 doping Nb 2 O 5 , 16 and adjusting the non-stoichiometry of YAG. 3 In fact, the ionic radius of Y 3+ ions is close to the ionic radii of rare-earth ions, providing the YAG ceramic with a wide range of ion substitution. 17 There could be appropriate ion doping methods to reduce the process difficulty of preparing the YAG ceramic and endow it with better properties to meet the needs of different scenarios.…”

“…As for the commissioning of ceramic performance, the moderate dielectric constant ( ε r ) determines the application environment, whereas the high‐quality factor ( Q × f ) ensures the device a wide range of frequency selectivity. In addition, the near‐zero temperature coefficient ( τ f ) reflects the device's operating stability 3–7 …”

Principal element design of garnets to access structure stability and excellent microwave dielectric properties

“…Zhou et al. optimized the preparation process of yttrium aluminum garnet ceramics and obtained excellent microwave dielectric properties of ɛ r = 11.0 ± 0.18, Q × f = 233 000 ± 4000 GHz, and τ f = 32.5 ± 3.4 ppm/°C 8,9 . This advantage allows such garnets to be used in high‐frequency wireless communications; however, those aluminates and gallates need extreme fabrication conditions (e.g., high densification temperature ∼1650°C for Y 3 Al 5 O 12 ) to achieve good physical performances.…”

“…4,5 More recently, some Ga/Al-based garnets have aroused research interest in their microwave dielectric properties due to their ultrahigh quality factors (e.g., Q × f ∼ 440 000 GHz for Y 3 Al 5 O 12 ; Q × f ∼ 192 173 GHz for Sm 3 Ga 5 O 12 ) 6,7 that are comparable to the complex perovskites. Zhou et al optimized the preparation process of yttrium aluminum garnet ceramics and obtained excellent microwave dielectric properties of ɛ r = 11.0 ± 0.18, Q × f = 233 000 ± 4000 GHz, and τ f = 32.5 ± 3.4 ppm/ • C. 8,9 This advantage allows such garnets to be used in high-frequency wireless communications; however, those aluminates and gallates need extreme fabrication conditions (e.g., high densification temperature ∼1650 • C for Y 3 Al 5 O 12 ) to achieve good physical performances. Hence, it is critical F I G U R E 1 (A) Crystal structure of A 3 B 2 C 3 O 12 garnet compound, (B) tolerance factor versus average electronegativity difference of garnet compounds to explore low-firing garnets for the practical application and promotion of such materials.…”