摘要
高频介质陶瓷材料在现代功能陶瓷材料中占有非常重要的地位,具有广泛的用途。高频介质陶瓷材料在高频(1MHz)下的介质损耗低、介电常数温度系数范围宽,广泛用作陶瓷电容器的电介质。根据介电常数温度系数可分为两大类：一类是热补偿电容器介质陶瓷材料。热补偿电容器介质陶瓷具有较大的负介电常数温度系数,如CaTiO3、TiO2等。热补偿电容器主要用在振荡回路里,以补偿回路电感元件的正温度系数,使回路谐振频率保持不变或变化很小。另一类是热稳定电容器介质陶瓷材料,其介电常数温度系数的绝对值很小,如TiO2-CaTiSiO5、CaTiO3-CaTiSiO5、CaTiO3-Ca(M g1/3Nb2/3)O3、SrZrO3-SrTiO3、CaTiO3-CaZrO3等。使用此类电介质材料制作的高稳定电容器广泛应用于移动通讯、卫星通讯、精密仪器和军用雷达等领域。其中CaTiO3-CaTiSiO5介质陶瓷是一种优良的高频介电陶瓷,它由单斜型CaTiSiO5(εr≈40,tanδ≈5×10-4,αε≈+1200×10-6/℃)和正交型CaTiO3(εr≈150,tanδ≈2.5×10-4,αε=-1800×10-6/℃)两相组成,具有较为优良的介电性能：εr≈82,tanδ≈4×10-4,αε≈±25×10-6/℃,因而日益受到关注。Ti02和CaTiSiO5以适当的摩尔比(0.82：0.18)进行复合也能够获得具有介电性能的复合材料,即较高介电常数、较低的介质损耗和接近于零的介电常数温度系数。
随着现代通讯技术的迅猛发展,陶瓷电容器也向小型化、大容量方面发展,而介电常数大、介质损耗小的介质陶瓷是制造高性能陶瓷电容器的前提条件。那么,提高CaTiO3-CaTiSiO5、(CaTiSiO5)0.18(TiO2)0.82陶瓷的介电性能是拓宽CaTiO3-CaTiSiO5、(CaTiSiO5)0.18(TiO2)0.82介质陶瓷应用范围的迫切课题。近年来,激光烧结技术在制备新材料和提高材料性能方面,显示出独特的优势。本工作采用激光烧结技术制备CaTiO3-CaTiSiO5、(CaTiSiO5)0.18(TiO2)0.82介质陶瓷,并采用X射线衍射(XRD)、扫描电子显微镜(SEM)、精密阻抗分析仪、拉曼散射等对材料的晶格结构、化学组成、微观结构、介电性能等进行测试与分析。
根据样品的物理性能和微观结构确定了激光烧结CaTiO3-CaTiSiO5、(CaTiSiO5)0.18(TiO2)0.82介质陶瓷的最佳工艺分别为：激光功率1.2 kW,离焦量90mm,烧结时间140s；激光功率1.0 kW,离焦量140 mm,烧结时间240s。
CaTiO3-CaTiSiO5陶瓷样品的介电性能与高温炉烧结相比,介电常数由炉烧的82提高到376,介质损耗和温度系数基本不变。微观结构也发生显著变化,样品比较致密没有大量的气孔和微裂纹,晶粒较大,生长完整并且呈树枝状定向生长,晶粒之间相互连成一体形成树枝状结构群。激光烧结的(CaTiSiO5)0.18(TiO2)0.82介质陶瓷致密度、纯度很高,形成了逆激光光束方向呈板条状规则生长的微观结构,有利于其介电性能的提高。在功能陶瓷的制备技术中,与其它定向生长技术相比激光烧结技术具有操作简单、晶粒定向生长强、效率高、致密度和纯度高等优点。
The high frequency dielectric ceramic materials has a very important position in modern functional ceramic materials, With a wide range of uses. Undering the high-frequency (1MHz) conditions The high frequency dielectric ceramic materials have low dielectric loss, wide range temperature coefficient of dielectric constant. It is widely used in ceramic capacitors dielectric. According to the temperature coefficient of dielectric constant It can be divided into two categories.One is the capacitor dielectric ceramic materials for thermal compensation,The capacitor dielectric ceramics of thermal compensation has a large negative temperature coefficient of dielectric constant.For example CaTiO3、TiO2 and so on.The capacitor dielectric ceramics of thermal compensation are used in the oscillator circuit into loop to compensate the positive temperature coefficient of inductance components, so that the resonant frequency circuit to maintain the same or little change.The other is thermally stable capacitor dielectric ceramics, It has a very small temperature coefficient of dielectric absolute value of the number, Such as TiO2-CaTiSiO5、CaTiO3-CaTiSiO5、CaTiO3-Ca(Mg1/3Nb2/3)O3、SrZrO3-SrTiO3、CaTiO3-CaZrO3 and so on.The thermally stable capacitor dielectric ceramics are widely used in mobile communications, satellite communications, precision instruments and military radar and other fields.The CaTiO3-CaTiSiO5 dielectric ceramic is an excellent high-frequency dielectric ceramics, It is monoclinic CaTiSiO5 (εr≈40, tanδ≈5×10-4,αε≈+1200×10-6/℃) and orthogonal CaTiO3 (εr≈40, tanδ≈5×10-4αε≈+1200×10-6/℃) two phases, It has a more excellent dielectric properties(εr≈82, tanδ≈4×10-4,αε≈±25×10-6/℃), Thus a growing concern. By the appropriate molar ratio (0.82:0.18) of compound TiO2 and CaTiSiO5 was also able to obtain a composite dielectric properties of composite materials, That has a high dielectric constant, low dielectric loss and near-zero temperature coefficient of dielectric constant.
Also with the rapid development of modern communication technology, Ceramic capacitors toward small, high-capacity areas direction.what's more, the dielectric ceramics of large dielectric constant and dielectric small loss is a prerequisite to create high-performance ceramic capacitors. Therefore, improving the dielectric properties of CaTiO3-CaTiSiO5、(CaTiSiO5)0.18(TiO2)0.82 dielectric ceramics is to broaden the scope of application of ceramic CaTiO3-CaTiSiO5、(CaTiSiO5)0.i8(TiO2)0.82 pressing issue. In recently years, laser sintering technology in the preparation of new materials and improve material performance shows a unique advantage. This work is the preparation of CaTiO3-CaTiSiO5 (CaTiSiO5)0.18(TiO2)0.82 dielectric ceramics using of laser sintering technology, and its preparation has been systematically studied. The lattice structure, chemical composition, microstructure, dielectric properties and so on were measured and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), precision impedance analyzer, Raman scattering et al measurement.
According to the physical properties and microstructure of the sample, The optimum technology of CaTiO3-CaTiSiO5, (CaTiSiO5)0.18(TiO2)0.82 dielectric ceramics by laser sintering were:Laser power 1.2 kW, defocus 90 mm, the sintering time 140s; laser power 1.0 kW, defocus 140 mm, sintering time 240s. CaTiO3-CaTiSiO5 dielectric properties of ceramic samples comparing with the high temperature furnace sintered, dielectric constant increased to 376 from 82 which the sample sintered by the furnace, dielectric loss and temperature coefficient basically unchanged. The microstructure changed significantly, the sample was dense without a large number of pores and micro-cracks, the grain was large and grew integrallty and alignmently, these grains connected each other and formed dendritic structure group. The density and purity of (CaTiSiO5)0.18(TiO2)0.82 dielectric ceramics are perfect, the sintered sample showed lath-shaped microstructure formed by regular growth with the laser beam in the opposite direction, which is beneficial to the improvement of dielectric properties. Among the techniques for formation of functional ceramics, compared with other orientated growth technology, the laser sintering technology is simple operation, strong orientated growth of grain, high efficiency, density and purity.
引文
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