The Raman Scattering Study Of PZT Ceramics

For many years laser Raman spectroscopy has been an importanttool for the investigation of microscopic molecular structure. Itsintensity, frequency shift, line width, charateristic peaks etc. haveclose relation with molecule's vibration, rotation, symmetry propertyand other information of fine-structure.1. Lead zirconate titanate ceramicsLead zirconate titanate (PbZr_1-xTi_xO₃ or PZT) ceramics is theperovskite solid solution of PbZrO3 and PbTiO₃, and has been theimportant and the most extensive application ferroelectric among allthe ferroelectric materials due to their excellent dieledtric,piezoelectric, pyroeletricty and many other properties. PbTiO3 isferroelectric with Curie temperature of 492 ℃ and PbZrO3 isantiferroelectric with Tc=232℃ . Such great differences attract people'sattention. PZT ceramics and its doping have been extensively studiedin recent years. Therefore, it's very important to analysis theprepareration technologyand the micro structure of PZT.Properties of material depend on its microstructure strongly. Leadzirconate titanate PbZr_1-xTi_xO₃ (PZT) with a perovskite structure hastetragonal, orthorhombic, and trigonal phases at room temperature,depending on the value of x, respectively, with the spacegroups C_4v¹, C_2v⁸, C_3v¹and C 36v, the latter two corresponding to twodifferent trigonal phases. At high temperature, PZT presents aparaelectric cubic phase (space group O_h¹). The phase diagram of PZTdetermined by Jaffe, Cook and Jaffe is show in Fig. 1-3. Themorphotropic phase boundary (MPB) at which the two adjacent phasesin the phase diagram (tetragonal and trigonal) have equal Gibbs freeenergy is also shown in Fig.1-3. However, the phases change abruptlyat the MPB only in the case of single crystals and, generally in apolycrystalline sample, there is a coexistence region between thetetragonal and trigonal phases. The width of the coexistence regionwas found to be inversely proportional to the size of the material. Nearthe MPB the dielectric constant, piezoelectric constant andelectromechanical coupling coefficient all exhibit a maximum value.Because of the tightly relationship of the microstructure and thepreparation technology of materials, several methods have beenemployed to prepare fine-sized PZTpowders.In the article, we choose the samples synthesised at MPB(x=0.52)by ball milling, solid-state calcination and high temperature hightpressue methods, respectively and use Raman technology to anylasisthe phase and the phase transition of the materials.Micro-Raman measurments were performed using a HR-800Jobin Yvon spectrometer. The process and results of the testing asfollows:â‘  Pb(Zr0.52Ti0.48)O3 powder had been synthesized from thecommercial PbO, TiO2 and ZrO2 powders using the ZrO2 ball millingtechnique in air at room temperature without any post-annealing. Thesynthesized powders milling for different hours were characterizedusing Raman spectra. PZT phase had not been formed from themixture of PbO, TiO2 and ZrO2 after milling 20h. After 40h, therewere a little PZT in the sample. After 60h, the formation of the PZTphase indicats the reaction of PbO, TiO2 and ZrO2 occurred during themilling process. The remained PbO, TiO2 and ZrO2was found in theRaman figure. Ultra-fine PZT phase can be obtained in the samplemilled for 80h and 120h. By the Raman analysis, we can see the twosamples have both tetragonal and trigonal phases.â‘¡ Sinter the sample ball milled 80h at 1100 ℃for 1h. The Ramanspectra of PZT were measured at room temperature. Byconcentation-freqency dependence of the vibrational modes, weidentified the sample have trigonal and tetragonal ferroelectric phasesat the same time. When the temperature rose to 420 ℃, the sample wasparaelectric cubic phase.â‘¢ Sample of PZT named P+Z+T was obtained through thesolid-state reaction from 99.9% pure PbO, ZrO2 and TiO2 oxides.From the Raman spectra, it can be identifed that the sample P+Z+Thave tetragonal and trigonal ferroelectric phases at room temperature.And at high temperature 420 ℃, the structure belongs to cubicparaelectric phase.â‘£ The "high temperature high pressue sample" called P+ZT. Theresult of Raman spectroscopy showed that the sample have tetragonaland trigonal ferroelectric phases at room temperature. At 420 ℃,thestructure was cubic.The results above research show that the samples ②③④ wemeasured are all fine PZT ceramics with two phases at roomtemperature and cubic phase at 420 ℃.Recently, a new phase has been discovered around MPB. Thus,the preparation technology and the studyof PZT microstructure is verymeaningful to be furthermore studied.2. quartzcoesite is a polymorph of silica, only stable at pressures inexess².5 Gpa at 500 ℃. At lower pressure it is thermodynamilallyunstable with respect to quartz. Before 1977, coesite was only knownfrom meteorite impact craters, in which it was formed from quartzduring high-pressures and temperatures generated by the impact andthen quenched sufficiently rapidly to prevent reversion to quartz.Coesite can also be readily synthesised from quartz in the laboratorybetween pressures of 3 and 9Gpa at high temperatures. Maincharacteristic of the transition is a change from space group P312 fora-quartz to C2/c which results from the building of four-ringschainsconsisting of [SiO4]4--tetrahedrals in the case of coesite.In this paper, 2Gpa320 ℃, 2Gpa800 ℃, 3.9GPa320 ℃and3.9GPa800 ℃ was used on?-SiO2 powder. The result of Ramanspectroscopy showed that the samples under 3.9Gpa synthesisedcoesite from quartz.The high-pressure phase transitions of SiO2 have long been ofinterest in earth science and materials science. A further research onthis work is obviouslynecessary.