Study On The Preparation And Properties Of CaCu₃Ti₄O₁₂ Ceramics Doped With Iron And Hafnium

In a wide frequency and temperature range,materials with high dielectric constant and low dielectric loss meet the requirements of micro-electronic integration and miniaturization of micro-electronic devices,such as capacitors,resonators and filters.As a common high dielectric constant material,the dielectric constant of giant dielectric ceramics CaCu₃Ti₄O₁₂?CCTO?can reach 10⁵ in the temperature range of 100 to 600 K.In the past decades,the research of CCTO ceramics has focused on dielectric properties,element doping is the most widely used method to obtain good dielectric properties.CaCu₃Ti₄-_x Fe_x O₁₂?0?x?0.5?,CaCu₃Ti₄-_x Hf_x O₁₂?0?x?0.25?,CaCu₃Ti₄-_x-y-y Fe_x Hf_y O₁₂?x=y,0?x+y?0.2?ceramics were prepared by molten salt method in this paper.Moreover,the influences of Fe and Hf doped samples on the morphology and properties of CCTO were investigated.Ceramic samples were tested by X-ray powder diffraction,scanning electron microscopy,dielectric spectroscopy,laser particle size analyzer,raman spectrometer and so on.In this paper,the percentage of EDS?Energy Dispersive X-Ray Spectroscopy?elements in pure phase CCTO are tested,which is consistent with the number of atoms in CCTO molecule,it shows that pure phase CCTO is successfully synthesized.Compared with the XRD?X-ray diffraction standard?PDF card of CCTO,Fe-doped ceramics at Ti site have eight obvious diffraction peaks,impurity peaks are not found.The results of SEM?scanning electron microscope?pictures infer that Fe-doped can change the size of the crystals,which may be due to the replacement of Ti⁺⁴ by Fe³⁺in CCTO lattice.The dielectric constant of low-doped CaCu₃Ti_4-x-x Fe_x O₁₂?0?x?0.04?ceramics decreases with the increase of x,and the dielectric loss peaks move to low frequency with the increase of x.Moreover,the dielectric constant of ceramics with high-doped amount?0.10?x?0.50?has no certain regularity with the change of frequency,and the dielectric loss peaks move to high frequency with the increase of x.The analysis of dielectric data makes a conclusion that the samples with the doped amounts of0.01 and 0.50 have better dielectric properties.When the doped amount is 0.01,the maximum dielectric constant is about 3.1×10⁴,and the maximum dielectric loss is about 3.51.When the doped amount is 0.50,the maximum dielectric constant is about 1.2×10⁴,and the maximum dielectric loss is about 3.04.At high temperature,the dielectric loss peaks of samples move to high frequency with the increase of temperature,and the dielectric constant increases with the increase of temperature.When the sample of doped amount is 0.02,the thermal activation energy is 0.465 eV,and thermal activation energy with doped amount of 0.04 is 0.479 eV.It indicates that Fe can be doped into CCTO ceramics in a certain amount.X-ray powder diffraction of Hf-doped CaCu₃Ti₄-_x Hf_x O₁₂?0?x?0.25?ceramics also have eight diffraction peaks,no microcrystalline phase is found.SEM analysis educes that Hf-doped ceramic samples have resulted in the smaller size of single crystal particles.At room temperature,the dielectric constant and the dielectric loss of Hf-doped samples decrease with the increase of x.The dielectric loss peaks of the samples occurs at about 10 MHz.When the samples of doped amounts are 0.20 and 0.25,two peaks of dielectric loss appear.When the doped amount of Hf is 0.02,the dielectric constant can reach 6.6×10⁴.At high temperature,Hf doped makes the dielectric loss peaks move to high frequency with the increase of temperature,and the dielectric constant increases with the increase of temperature.The thermal activation energy of Hf doped?x=0.02?sample is 0.764 eV,and Hf doped?x=0.04?is0.796 eV.It shows that Hf can be doped into CCTO ceramic.Compared the dielectric constant of CaCu₃Ti₄-_x-y-y Fe_x Hf_y O₁₂?x=y,0?x+y?0.2?ceramics and single-doped Fe?Hf ceramics,Hf-doped ceramic has the largest dielectric constant,it can reach 8.8×10⁴.The dielectric loss peaks of Hf-doped samples occur in the high frequency region,while those of Fe-doped and co-doped samples occur in the low frequency region.SEM analysis shows that the average size of Fe-doped crystal particles is larger than that of Hf-doped and co-doped crystal particles.At high temperature,the dielectric constant of both single-doped and co-doped ceramic samples increase with the increase of temperature,and the dielectric loss peaks move to high frequency with the increase of temperature.It is also found that loss value of dielectric loss peak of Fe-doped sample is mainly around 5,Hf-doped sample is about 3,and co-doped sample is between single-doped,about 4.The thermal activation energy of the sample with co-doped amount?x=y=0.02?is 0.582 eV,and the thermal activation energy is 0.596 eV for the co-doped amount?x=y=0.04?.It shows that Fe and Hf can also be co-doped into CCTO ceramic.