稀土氧化物掺杂对Ba0.6Sr0.4TiO3-MgO复合物结构及微波介电性能的影响

研究了不同质量分数(0~1.5%)的各种稀土氧化物对Ba0.6Sr0.4TiO3(40%)-MgO(60%)陶瓷微观结构和介电性能的影响.研究表明,大半径的稀土离子掺杂能有效降低材料的介电常数并提高品质因数;而小半径的稀土离子掺杂则会提高材料的微波介电损耗.当掺杂量超过0.2%时,所有样品的调谐率都随着添加量的增加而下降.与未掺杂的BST-MgO相比,0.2%稀土掺杂样品的调谐率变化规律及机理随掺杂物的不同而不同:Nd2O3和Yb2O3 掺杂样品中调谐率的大幅度升高归因于结电容的贡献,Sm2O3 掺杂样品调谐率的下降主要由MgO晶粒的聚集所致,而Y3+同时占据A位和B位引起了样品调谐率的下降.研究发现在BST-MgO中添加具有大离子半径的稀土氧化物(如La2O3、CeO2、Nd2O3、Sm2O3)并优化其添加量,能满足铁电移相器等微波调谐器件的要求.

Influence of Rare-earth Oxide Dopants on Microstructure and Microwave Dielectric Properties of Ba0.6Sr0.4TiO3-MgO Compound

40wt%Ba0.6Sr0.4TiO3- 60wt%MgO ceramics with 0~1.5wt% various rare-earth oxides prepared by a conventional ceramic processing method were investigated. A strong correlation among the microstructure, microwave dielectric properties and rare-earth oxide dopants was observed. The results indicated that the large ions rare-earth additions effectively decreased the dielectric constant and improved the microwave qualify factor at microwave frequency, while the small rare-earth ions dopants deteriorated the dielectric loss greatly. When the doping content exceeded 0.2wt%, the tunability decreased with the doping amount increase in all samples. Comparing with the undoped BST-MgO, the tunabilty of 0.2wt% doped samples varied irregularly with various rare-earth oxides. In the 0.2wt% Nd2O3 and Yb2O3 doped samples, the junction capacitors were responsible for the higher tunability, while the non uniform distribution of MgO grains caused the great decrease of tunability in 0.2wt% Sm2O3 doped samples. In the 0.2wt% Y2O3 doped sample, the decrease of tunability was due to the Y3+ ions occupied both the A-site and B-site. Choosing the appropriate rare-earth oxides (La2O3, CeO2, Nd2O3 and Sm2O3) and optimizing doping amount could satisfy the tunable microwave devices application such as the ferroelectric phase shifters.