钙钛矿型钛酸钡基纳米晶的合成、介电性能及高温改性研究

THE STUDY OF SYNTHESIS，DIELECTRIC PROPERTY AND HIGH-TEMPERATURE MODIFICATION OF PEROVSKITE BARIUM TITANATE-BASED NANOCRYSTALS

周玉霞

11649064

硕士

化学

黄立民

2018

2018.7.10

哈尔滨工业大学

深圳

钙钛矿结构氧化物是一种典型的无机介电材料，在电子器件方面有广泛的应用，从而受到了人们的重点关注。而纳米尺度的钙钛矿晶由于在聚合物基底里良好的分散性，能减小颗粒的团聚程度，从而使得复合薄膜外观平整，内部致密，其介电强度和能量密度显著提高，因此它是制备高介电性能复合薄膜不可或缺的材料之一。同时钙钛矿纳米晶的小尺寸对于电子器件的小型化具有重要意义。钛酸钡（BaTiO3）是一种典型的具有钙钛矿结构的氧化物，在电子工业上有着广泛的应用，因此本文着重研究BaTiO3及与其相关的钙钛矿纳米晶的合成、介电性能以及高温改性。主要研究内容包括：一、单分散方形钙钛矿型钛酸钡基纳米晶的合成及表征用溶剂热法在180 ℃下反应48 h合成了BaTiO3、SrTiO3、Ba1-xSrxTiO3、La掺杂BaTiO3、以及Ba0.85La0.05Sr0.1Ti0.9875O3纳米晶，经TEM、XRD表征证明这些纳米粒子均是单分散的立方形单晶，没有BaCO3杂质存在。XRD结果显示BaTiO3纳米晶在长程有序上表现为立方相，但Raman分析表明晶体中在短程有序上仍有四方相存在。TGA和FT-IR分析说明纳米晶表面大概有30 wt%的油酸配体存在，所以能使纳米晶在非极性溶剂如甲苯中形成稳定的胶体溶液，放置几个月都不会沉淀或团聚。二、单分散方形钙钛矿型钛酸钡基纳米晶的介电性能研究从上述合成的样品中挑选出四个有代表性的样品BaTiO3、SrTiO3、Ba1-xSrxTiO3、1 mol%La掺杂BaTiO3制成薄片对其进行介电性能测试，考虑到薄片没有经过高温烧结形成陶瓷片，内部充满了空气，测量出的薄片有效介电常数并不能反映纳米晶的实际介电常数，所以引入布鲁格曼有效介质模型计算并比较了各个纳米晶的实际介电常数，并且探究了其原因。计算出的结果显示SrTiO3和1 mol%La-BaTiO3这两个样品的相对介电常数随着频率的升高分别降低了68%和63%，而BaTiO3和Ba0.6Sr0.4TiO3的相对介电常数在整个频率范围内较稳定，分别降低了15%和29%左右。Ba0.6Sr0.4TiO3晶胞有局部结构畸变，增加了电场极化，导致Ba0.6Sr0.4TiO3纳米晶的相对介电常数大于BaTiO3的相对介电常数。1mol％La掺杂的BaTiO3纳米晶内的La3+占据Ba位点，诱导Ti位点产生空位，从而增大电场极化，导致室温下的相对介电常数大于BaTiO3的。三、钛酸钡纳米晶的高温改性用聚合物单体在纳米晶的溶液中进行聚合，将聚合物充分包裹在纳米晶表面，纳米晶在氮气等惰性气氛下进行高温焙烧，聚合物转变成碳，包裹在纳米晶表面，阻止纳米晶团聚，再在低温下烧掉碳，得到纯的BaTiO3纳米晶。经XRD和Raman分析表明，高温改性的纳米晶的四方相含量提高了，并且在TEM图上可以看到，与原粉对比直接在800 ℃高温焙烧的样品团聚严重，而加了聚合物的样品，分散性较好。并且此方法适用于其他钙钛矿纳米晶。

Perovskite oxides as a kind of typical inorganic dielectric material have been widely used in electronic devices, thus having attracted people’s attention. The perovskite nanocrystals can enhance its dispersion and reduce its agglomeration in the polymer matrix so that the nanocomposite thin films own flat appearances and internal higher density. Therefore, the dielectric strength and energy density of the nanocomposite films are significantly improved. For this reason, it is one of the indispensable materials for preparing nanocomposite films with excellent dielectric properties. At the same time, the small size of perovskite nanocrystals can reduce the size of the device, which is of great significance for the miniaturization of electronic devices.Barium titanate (BaTiO3) which is a typical oxide with a perovskite structure has a wide range of applications in the electronics industry. Therefore, this paper focuses on the study of synthesis, dielectric properties and high temperature modification of BaTiO3 and its related perovskite nanocrystals.The main research content includes:I. Synthesis and characterization of monodispersed cubiodal perovskite barium titanate-based nanocrystalsBaTiO3, SrTiO3, Ba1-xSrxTiO3, La-doped BaTiO3 and Ba0.85La0.05Sr0.1Ti0.9875O3 nanocrystals were synthesized by solvothermal method at 180 ℃for 48 h. The TEM and XRD results indicate that the nanocrystals which are single-crystalline and non-aggregated are uniform in size and high degree in purity. The XRD results show that the BaTiO3 nanocrystals are cubic phase in long-range order, but Raman analysis shows that there are still tetragonal phases in the short-range order. TGA and FT-IR analysis demonstrates that about 30 wt% of oleate ligand is coated on the surface of the nanocrystals, so that the nanocrystals can form a stable colloidal solution in nonpolar solvents such as toluene for several months.Ⅱ. The study of dielectric properties of monodispersed cubiodal perovskite barium titanate-based nanocrystalsFour representative samples BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3, 1 mol% La-doped BaTiO3 were selected from the above synthesized samples for dielectric property study. Considering that the thin flakes were not sintered at high temperature to form ceramic flakes and the interior was filled with air, the measured effective dielectric constant could not reflect the intrinsic dielectric constant of the nanocrystals. Therefore, the actual dielectric constant of each nanocrystal was calculated and compared by introducing the Brugmann’s effective medium model, and the related principle was explored.The calculated results show that with the increase of the frequency the relative dielectric constants of SrTiO3 and 1 mol% La-BaTiO3 are significantly reduced by 68% and 63%, respectively. The relative dielectric constant of Ba0.6Sr0.4TiO3 and BaTiO3 are relatively stable over the entire frequency range, and they are reduced by about 15% and 29%, respectively. The dielectric constants of 1 mol% La-BaTiO3 and Ba0.6Sr0.4TiO3 nanocrystals are larger than that of BaTiO3. The relative dielectric constant of Ba0.6Sr0.4TiO3 nanocrystals increased a lot compared with BaTiO3 nanocrystals because of the local structural distortion of Ba0.6Sr0.4TiO3 crystal cell which increases the electric field polarization and result to enhanced dielectric constant. The reason why the 1 mol% La-doped BaTiO3 sample exhibits an enhanced relative dielectric constant is that the incorporation of La3+ in the BaTiO3 nanocrystals occupies Ba site and induces Ti vacancy, thereby strengthening the electric field polarization and increasing the relative permittivity at room temperature.Ⅲ. The high-temperature modification of BaTiO3 nanoparticlesThe polymer monomer was polymerized in the nanocrystals solution, which caused the polymer to be fully wrapped on the surface of the nanocrystals. The nanocrystals were first subjected to high temperature modification in an inert atmosphere such as nitrogen gas. At high temperatures, the polymer was converted to carbon and encapsulated on the surface of the nanocrystals, which prevented the agglomeration of the nanocrystals. And then the carbon was burnt at a low temperature in order to obtain the pure BaTiO3 nanocrystals. XRD and Raman analysis showed that the content of the tetragonal phase in the high temperature modified nanocrystals was increased. And it can be seen from the TEM image that compared with the original powder the samples directly calcined at high 800 °C are heavily agglomerated, while the polymer-added samples are better dispersed. Moreover this method is appliable for other perovskite nanocrystals.

钛酸钡 溶剂热法 掺杂 介电性能 高温改性

barium titanate solvothermal doping dielectric propertie high-temperature modification

中文

联合培养

南方科技大学

周玉霞. 钙钛矿型钛酸钡基纳米晶的合成、介电性能及高温改性研究[D]. 深圳. 哈尔滨工业大学,2018.