Sr Katkılı Kurşun Zirkonat Titanat Tipi Piezoseramiklerin X Işınları Difraksiyonu Ve Taramalı Elektron Mikroskobu İle Karakterizasyonu

Abstract

Bu çalışmada Sr katkılı kurşun zirkonat (PZT) tipi piezoseramiklerde bileşimsel farklılığın ve sinterleme şartlarının yapıya etkileri incelenmiştir. Çalışmada ağırlıkça % 0.012 ile %0.018 arasında değişen oranlarda Sr katkısı kullanılmış ve numunelerdeki Zr02/Ti02 oranı da 1.13 ile 1.63 arasında değiştirilerek üç faklı sinterleme şartında numunelerin yapısal değişimleri incelenmiştir. (Pbo.9lSro.Os)(Zro.62Tİo.38)03, (Pbo.8lSro.o9)(Zro.S3Tİo.47)03 Ve (Pb0.94Sr0.06)(Zro.53Tİo.47)Q3 şeklinde üç farklı bileşim ve 1220 °C/2 saat, 1220 °C/3 saat ve 1240 °C/1 saat, olmak üzere üç farklı sinterleme şartında deneyler gerçekleştirilerek bileşimin ve sinterleme şartlarının etkileri gözlenmiştri. Sr katkılı PZt numune üretimi öğütme, kalsinasyon ve sinterleme ana kademelerinden oluşan konvansiyonel yöntemle yapılmıştır. Karakterizasyon çalışmaları ise X ışınları difraktometresi (RIGAKU RİNT DMAX-1000) ve taramalı elektron mikroskobu (JEOL JSM-840) ile gerçekleştirilmiştir. X ışınları difraksiyonu (XRD) ile gerçekleştirilen analizlerin sonuçları beklenenlerle uymuludur. En yüksek Zr02/Ti02 oranına sahip numunenin rhombohedral yapıda olduğu bulunmuştur. XRD sonuçları ayrıca Sr katkısının yapıya en iyi 1220 °C'de 3 saat sinterleme şartında girdiğini göstermiştir. Sinterleme şartlarının etkinliği taramalı elektron mikroskobu (SEM) çalışmaları ile de gösterilmiştir. 1220 °C'de 3 saat sinterleme şartında yapıdaki porlarda küçülme ve küreselleşmenin baskın olduğu gözlenmiş ve bu sinterleme şartının en uygun koşul olduğu bulunmuştur

Single crystals such as, Rochelle salt and quartz, were the first materials that display a piezoelectric effect. However, since the discovery of a strong piezoelectric effect in the lead zirconate titanate solid solutions in 1950's [1], this family of ceramics with various additives became one of the most popular and commonly used piezoelectric material. Since then hundreds of new piezoelectric materials with various crystal structures have been reported. As it is in all other materials, crystal structure and microstructure of piezoelectric materials plays an important role in the final piezoelectric properties. In this work X-Ray diffraction analysis were carried out to determine the effect of Sr dopant content, the Zr02/ Ti02 ratio and the sintering conditions on the crystal structure of Pb(ZrTi)03 type piezoceramics. Microstructural characterization were~done by examination of the samples using a Scanning Electron Microscope. The microstructure and, the size, shape, type and distribution of pores were determined through these examinations. Porosity and surface roughness are crucial parameters in the processing of piezoceramic materials and final properties are directly affected by these parameters. Increasing porosity causes decreasing dielectric constant in piezoceramics. Also the resonance frequency of a piezoelectric transducer depends on the geometry and the dimensions of the ceramic piece. Therefore, precise machining of the ceramic is very important. Machining of these pieces are usually done by grinding and lapping. During machining processes, coolants can penetrate easily into a porous material and decrease the dielectric constant. Application of an electrode layer on the surfaces of the piezoelectric material is another step of transducer fabrication. This electrode layer can be applied by different techniques, but the control of porosity before electroding is necessary to obtain high quality electrodes on surfaces. Adhesion of electrodes and presence of air gaps between electrode and ceramic body is directly affected by porosity. Lower adhesion of electrode may cause peeling of electrode due to vibration in working conditions. Presence of air gaps between electrode layer and ceramic body lowers the capacitance of a ceramic transducer [1]. XI 2. SAMPLE PROCESSING: PbO (Merck product), SrC03 (Merck product), Zr02 (Fluka product) and Ti02 (Merck product) were used as raw materials. Samples were processed through conventional calcination route. Processing included ball milling (in water media), calcining (at 850 °C for 4 hours), shaping via hydraulic pressing and sintering under normal atmosphere. Flow diagram of sample processing is shown in Figure 1. MIXING (3 hrs - water) ' PbO adding (for to replace evaporated PbO | during calcination) I ) CALCINATION (850 °C/ 4 hrs) i MIXING (6 hrs - water) I SHAPING Î SINTERING (1220°C/2hrs) (1220°C/3hrs) JgMPC / 1 hrt J J J f ELECTRICAL \ OPERATIONS I 1 (elcctroding, poling) J H XRD & SEM ANALYSIS J Figure 1 : Sample processing flow diagram. Xll Three different compositions were used in this work as follows; PZT-A : (Pbo.9iSro.o9)(Tio.47Zro.53)03 PZT-K : (Pb0.9iSro.o9)(Tio.38Zro.62)03 PZT-C : (Pbo.94Sro.o6)(Tio.47Zro.53)03 These compositions have been chosen to observe effects of Strontium dopant content (PZT-K and PZT-A) and Zr02/Ti02 ratio (PZT-A and PZT-C). 3. XRD ANALYSIS: XRD analysis were carried out to observe the effects of Zr02/Ti02 ratio (Zr02 / Ti02 = 1. 1 3 for PZT-C and PZT-A ; Zr02 / Ti02 = 1.63 for PZT-K) and amount of Sr dopant (0.018 % in weight for PZT-K and PZT-A ; 0.012 % in weight for PZT- C) on phase transformations. Three main phases exist in lead zirconate titanate solid solution for various PZ to PT ratios according to PbZr03 - PbTi03 binary diagram (Figure 2). Diagram aiso shows the compositional locations of samples. As it is also determined by XRD analysis the composition PZT-A and PZT-C have a tetragonal structure, and PZT-K has a rhombohedral structure at room temperature. O IO 20 30 40 50 60 70 PbZr03 Mole % PbTi03 Figure 2: PbZr03.PbTi03 binary diagram [1] 90 IOC PbTiO- XU1 As a result of having tetragonal structure, samples PZT-A and PZT-C have showed different d values for 001 and 100 planes at 26 values from 20° to 30° (Figures 3-8). On the other hand sample PZT-K displays only one clear peak in the same 20 region. This clearly indicates that the sample has a rhombohedral structure [3] which has been caused by high Zr02 / Ti02 ratio. Zr+4 substitution instead of Tf4, reduces the tetragonal distortion in PbTi03 and results in the appearance of rhombohedral structure [1]. This can be seen in the XRD diagrams given in figures 3 to 8. Diagrams were presented for each sample which were sintered at three different conditions and also presented for each sintering condition. XRD analysis indicated that samples PZT-A and PZT-C both have a tetragonal crystal structure and PZT-K has a rhombohedral structure for all sintering conditions, and strontium substitution is more efficient for samples which were sintered at 1220 °C - 3 hr. sintering condition. XIV to CO I Ü o o CM CM T- CD TD CD i_ © Ç "to CD CO Q. E CD (0 "cc.B to c aj ra o. c o =0 CO ? * > X .zzo 4 zzo ^ zzo zvv zi\, h < zvv û zoo i zoo zoo 4 vvv vvvA ^ l- 01- vvv A 1-Ot vov 13 too < too too 4 V) c o TJ c o u 0) 3 g (0 > CD ?o (D 1_ (D TJ (D t_ (D C < û. a. E (0 CO.*- o CO E £ o. c o ""S CO i b *. ozz ZZO UZ zu m zu VVİ pot tot on. 00». J i-oo ^ oov y too «<. OOP 1.00 ^ CO c g c o Ü CO o CD > CO T3