Terahertz Dielectric Properties Of CaCu₃Ti₄O₁₂ Ceramics

CaCu₃Ti₄O₁₂（CCTO） ceramics have been widely concerned because of their high dielectric constant and potential applications in the future. At present, the main problem of CCTO ceramics is the high dielectric loss, which limits its practical application in the business. In order to solve this problem, I have done work by theoretical simulation and experiment,which has three parts:（1） Numerical simulation of the basic dielectric properties of CaCu₃Ti₄O₁₂ ceramics;（2） Terahertz dielectric properties of CaCu₃Ti₄O₁₂ ceramics;（3） Modulation of dielectric properties of Nd2O3 doped CaCu₃Ti₄O₁₂ ceramics at terahertz region.In the first part, using the computer to simulate the calculation. The energy and optical properties of CCTO are calculated by using the most advanced material simulation software Materials Studio. The results of Simulation are: the establishment of CCTO structure model firstly, and then using the Reflex module software, obtaining the CCTO diffraction pattern（XRD pattern）. Then by the CASTEP module software, getting the CCTO energy band diagram, the density of States and optical properties of map of CCTO also be obtained. Finally, the calculation results were analyzed to come to conclusion.In the second part, owing to the rapid development of capacitor for terahertz（1 THz = 1012 Hz） electronics, the THz dielectric properties of different granular CCTO ceramics are investigated experimentally. It is found that the dielectric constant εr of CCTO of small particles（Φ < 2μm） is below 700, while exceeds 2000 for larger granular（Φ > 10μm） CCTO in the frequency range below 1 MHz. Correspondingly, the dielectric loss of CCTO is from 0.1 to 0.6. In THz frequency, however, different granular CCTO ceramics exhibts the same value of εr（εr=72±3）. Here, the ionic polarizability dominated εr so that it is insensitive to the grain-size of CCTO. However, the larger grain-size increases the scattering cross-section, which enlarger the total extinction ratio of transmission so as to increase the dielectric loss in THz frequency range. It is found the small granular CCTO is a potential dielectric materials for the application of THz capacitors.In the third part, the modulation of dielectric constant and loss at terahertz（THz） frequency of CCTO ceramics is achieved by doping Nd2O3. Nd2O3 doped CCTO samples are prepared by solid-state reaction method. Structure analysis shows that the Nd ions do not affect the basic crystalline structure of CCTO. With the help of morphologic characterization, one can find that grain size increase when increasing the concentration of Nd2O3 first. But it decrease when the concentration of Nd2O3 exceed 0.6 wt%. An evident refinement effect occurs when the concentrations of Nd2O3 increase monotonically. THz spectroscopic measurement shows that the variation of real part of dielectric constant is contrary to that of grain-size of CCTO, while the loss variation is in agreement with the trend of grain-size variation. Our results indicate that the dielectric constant at THz frequency of CCTO ceramics can be modulated effectively by doping Nd2O3.