【作者】 田义良；

【导师】 陈湘明；

【作者基本信息】 浙江大学 ， 材料学， 2010， 硕士

【摘要】 双钙钛矿陶瓷由于其优越的物理性能特别是磁学性能而备受关注。为了更好地理解双钙钛矿陶瓷的电学和磁学性能,本文通过对双钙钛矿陶瓷Nd₂CoMnO₆的介电性能,特别是介电弛豫特性的研究,探索其介电弛豫的物理本质,研究其铁磁性转变机制。同时,探索了利用脉冲激光沉积法（PLD）在Pt/TiO₂/SiO₂/Si基板上制备双钙钛矿La₂NiMnO₆薄膜的制备条件对薄膜的影响规律。采用固相反应法制备了Nd₂CoMnO₆致密陶瓷,Nd₂CoMnO₆陶瓷在133-300 K温度区间存在一个介电弛豫现象,其符合德拜模型,属于典型的德拜弛豫。利用Arrhenius定律拟合得到弛豫时间与激活能分别为τ₀=3.41 ns和Ea=0.19 eV,该激活能为电子从Co²⁺到Mn⁴⁺跃迁所需激活能。Nd₂CoMnO₆陶瓷存在两个铁磁转变温度,高温的T_c1=150 K和低温的T_c2=136 K,高温铁磁转变是由于Co²⁺-O-Mn⁴⁺相互作用引起的,而低温铁磁转变则是由电子从Co²⁺到Mn⁴⁺跃迁导致部分区域Co³⁺的存在引起的。采用脉冲激光沉积法（PLD）在Pt/TiO₂/SiO₂/Si基板上制备出了La₂NiMnO₆薄膜。在基板温度873K时,氧气压从50Pa到150Pa都可获得单相的La₂NiMnO₆薄膜,在基板温度923 K时,氧气压从50Pa到100Pa都可获得单相的La₂NiMnO₆薄膜。在低于873 K时会有非晶体的产生,而在高于923 K时气压变化会导致其它杂相的形成。在同一温度下,随着氧气压的升高,薄膜沉积速度逐渐减小,薄膜晶粒更加紧密均匀排列。在同一气压下,随温度的升高,热应力的增大造成薄膜晶粒之间的分裂,从而薄膜表面裂纹逐渐增加。所以利用PLD在Pt/TiO₂/SiO₂/Si基板上制备La₂NiMnO₆薄膜,在脉冲频率3 Hz,基板温度为873K,气压为150Pa时可以获得良好的La₂NiMnO₆薄膜。更多还原

【Abstract】 Double perovskite ceramics have attracted much attention because of the excellentphysical properties, especially the magnetic properties. For the better understanding ofthe nature of electric and magnetic properties, Nd₂CoMnO₆ ceramics wereinvestigated to determine the physical nature of dielectric relaxations, the dielectricand magnetic characteristics. Meanwhile, La₂NiMnO₆ double perovskite films wereprepared by Pulsed Laser Deposition on Pt/TiCVSiCVSi substrate under differentdeposition conditions to pursue the best one.Dense Nd₂CoMnO₆ ceramics could be obtained by a solid state reaction process.A giant dielectric constant peak with strong frequency dispersion was observed, andthe corresponding dielectric relaxation was well fitted with the modified Debyeequation, and the parametersτ₀=3.41 ns and Ea=0.19 eV were obtained by theArrhenius fitting. The activation energy Ea is close to the energy required to transferan electron from Co²⁺ to Mn⁴⁺. Two ferromagnetic phase （FM） transitions weredetermined at the temperature of 150 K (T_c1) and 136 K (T_c2), respectively. Where,Tcl is the result of the interactions between Co²⁺-O-Mn⁴⁺, and T_c2 is related to theexistence of Co³⁺ resulting from an electron transfer from Co²⁺ to Mn⁴⁺.La₂NiMnO₆ thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by the pulsedlaser deposition process. The temperature and the oxygen pressure played the primaryrole dominating the crystallization behavior and the morphology of La₂NiMnO₆ thinfilms. The well crystallized La₂NiMnO₆ thin films could be obtained at 873K and 923K under all oxygen pressures investigated here, and the fine morphology was obtainedunder the oxygen pressures equal to or higher than 50 Pa and 100 Pa, respectively.When the temperature was lower than 873 K or higher than 923 K, the wellcrystallized single phase La₂NiMnO₆ thin films could not be obtained. So pursuingthe best deposition condition is the most critical requirement for the high quality of thin film.更多还原