摘要
研究了CeO2添加量对(Pb0.48Ca0.52)(Fe0.5Nb0.5)O3微观结构及介电性能的影响。研究表明:当Ce4+含量≤2.2%(摩尔分数,下同)时,样品为单一钙钛矿相,并且Ce4+进入A位造成样品晶胞的收缩,而Ce4+进入B位造成样品晶胞的膨胀。当Ce4+含量>2.2%时,样品中会出现未知相。样品介电常数随Ce4+含量的增加先增大,后减小,介电常数的增大是由于晶胞体积的收缩以及相对密度的增大;减小则是由于Ce4+的半径(0.087nm)大于(Fe3++Nb5+)的平均半径(0.064nm)以及体系中未知相的出现。此外,由于Ce4+的取代造成氧空位消除、相对密度增大以及晶粒尺寸增大,从而当Ce4+的含量超过一定值时,样品的品质因数得到提高。样品谐振频率温度系数随Ce4+取代量的增加先迅速下降,然后又逐步增加。这是由于Ce4+的取代使得B位键价增加,谐振频率温度系数τf下降;但当样品中出现未知相时,τf又增加。当Ce4+的含量为2.2%时,τf达到最小值3.5×10-6/℃,且此时样品介电常数εr及品质因数谐振频率的积Qf值分别为93.7,6770GHz。研究了CeO2添加(Pb0.48Ca0.52)(Fe0.5Nb0.5)O3样品中晶体结构与介电性能之间的关系。
The crystal structure and microwave dielectric properties of (Pb0.48Ca0.52) (Fe0.5Nb0.5)O3 ceramics added with CeO2 was investigated. Results show that when the molar fraction of doping CeO2 is &le2.2%, the cell volume will contract by entering Ce4+ into the A-site of the samples with single perovskite phase, while the cell volume will expand by entering Ce4+ into B-site. An unknown phase will appear when the molar fraction of doping CeO2 is ≥2.2%. The dielectric constant of the sample increases with the increase of the molar fraction of doping CeO2 in the range from 0 to 1.5%, because of the contraction of cell volume and the increase of relative density then decreases because of the larger ionic radius of Ce4+ (0.087 nm), compared to the average radius of (0.064 nm) of (Fe3++Nb5+), and appearance of an unknown phase in sample. The product Qf of quality factor and resonance frequency firstly decreases as Ce4+ is in the range of 0 to 0.1% for molar fraction of CeO2 then gradually increases because of the elimination of oxygen vacancies, increase of relative density and the greater grain size. After the appearance of the unknown phase when molar fraction of CeO2 exceeds 2.2%, Qf decreases again. The temperature coefficient of resonant frequencies τf can be effectively controlled via the strengthened B-site bond valence as Ce4+ content in the range of 0 to 2.2%, and when the unknown phase appears in ceramics, τf value increases. (Pb0.48Ca0.52) (Fe0.5Nb0.5)O3 ceramics with nearly zero of τf can be obtained in 2.2% CeO2 doping, and the dielectric constant and the Qf value of the ceramics are 93.7 and 6770 GHz, respectively.
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2004年第6期709-713,共5页
Journal of The Chinese Ceramic Society
基金
国家863项目(2001AA101C01)
2002湖北省科技攻关计划(2002AA101C01)资助项目
关键词
钙钛矿结构
晶胞体积
介电常数
品质因数
谐振频率温度系数
Additives
Ceramic materials
Crystal lattices
Crystal structure
Dielectric properties of solids
X ray diffraction analysis
