Electrocaloric effect of inorganic low temperature sintering (Pb ceramics

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1 IOP Conference Series: Materials Science and Engineering PAPER OPEN ACCESS Electrocaloric effect of inorganic low temperature sintering (Pb 0.88 La 0.08 )(Zr 0.65 Ti 0.35 )O 3 ceramics To cite this article: Cheol-Min Ra et al 2015 IOP Conf. Ser.: Mater. Sci. Eng View the article online for updates and enhancements. This content was downloaded from IP address on 31/01/2019 at 18:09

2 Electrocaloric effect of inorganic low temperature sintering (Pb 0.88 La 0.08 )(Zr 0.65 Ti 0.35 )O 3 ceramics Cheol-Min Ra 1, Ju-Hyun Yoo 1, 3, Seung-Hun Chol 1 and Jie-Young Lee 2 1 Semyung University, Jecheon , Republic of Korea 2 Department of Computer Science, Semyung University, Jecheon , Republic of Korea juhyun57@semyung.ac.kr Abstract. In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, (Pb 0.88 La 0.08 )(Zr 0.65 Ti 0.35 ) O3 ceramics were fabricated by the conventional solid-state method. Electrocaloric effects of inorganic (Pb 0.88 La 0.08 )(Zr 0.65 Ti 0.35 )O 3 ferroelectric ceramics were investigated and discussed using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to 220. The temperature change T due to the electrocaloric effect was calculated by Maxwell s relations. The temperature change T of ceramics sintered at 950 reached the maximum of ~0.19 at 190 under applied electric field of 30 kv/cm. 1. Introduction In recent years, temperature of the earth has been gradually increased because of its global warming. As a result, the use of refrigerators and air conditioners has been increasing. Therefore, the usages of Freon gas have been also increasing. It is well known that Freon gas is the major cause of the destruction of ozone layer due to Greenhouse effect. Accordingly, in order to protect the global environment, the substitute material for Freon gas is urgent [1]. However, perfect substitute materials for Freon gas have not yet been found. Electrocaloric (abbreviated as EC) effect as a new refrigeration technologies has been received the attention of many researchers. Unlike other solid-state refrigeration technologies, ferroelectric cooler based on the principle of EC effect could be small size and environmentally friendly [2-4]. The EC effect is a change of temperature in a dielectric material by the change in entropy on application of electric field [5, 6]. It is well known that change of entropy in ferroelectric material is maximum near the phase transition temperature because a high change in polarization in vicinity of the transition temperature [7, 8]. In order to utilize the high EC effect at room temperature, research on ferroelectric with low curie temperature has been carried out. PZT based ferroelectric shows outstanding EC effect. For example, Mischenko et al. observed refrigeration temperature change of ~12k in PZT thin films. Lu et al. also observed that thin films of PLZT and polymer exhibit a refrigeration temperature change of 20K and 40K under an electric field of 120 kv/mm, 160 kv/mm, respectively [9, 10]. 3 Address for correspondence: Ju-Hyun Yoo, Semyung University, Jecheon , Republic of Korea. E- mail: juhyun57@semyung.ac.kr. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1

3 In this work, in order to t develop ferroelectric ceramics with outstanding EC effect, (Pb 0.88 La 0.08 )(Zr 0.65 Ti 0.35 )O 3 ceramics were prepared by a conventional solid-state reaction method and then ferroelectric and ECE properties were investigated by using characteristicc cs of P-E hysteresis loops to measure EC effect. 2. Experimental procedure The compositions used in this study were as follow; (Pb 0.88 La 0.08 )(Ti 0.65 Zr 0.35 )O 3 + sintering aid (Bi 2 O3 + CuO + Lii 2 O 3 ) (1) The (Pb 0.88 La 0.08 )(Ti 0.65 Zr 0.35 ) O 3 ceramicss was fabricated by using a conventional mixed oxide process. The raw materials, PbO (99.5%), La 2 O 3 (99.99%), TiO 2 (99%),( ZrO 2 (99%) compositions were weighed by mol ratio synthesize the given composition and the milled for 24h using a zirconia ball in acetone. After drying, they were calcined at 850 for 2 h and then, the calcined powder remixed with sintering aid and dried again. A polyvinyl alcohol (PVA: 5 wt% aqueous solution) was subsequently added to the dried powder, thee well mixed powder were into a diskk (Φ17 mm) ) at under pressure of 15 Mpa. After burned out at 600 for 3 h, specimens were w sinteredd at 950 and 970 for 4 h in air. The surfaces of specimen were electrode by silver electrode and fired at 600 for f 10min. P-E hysteresis loops were measured by usingg Sawyer-Tower circuit for range of temperature from f near room temperature to 220 and temperaturee change ( T) were calculated by indirect measurement method using Maxwell s relation. 3. Results and discussion Figure 1 shows the temperature dependence of dielectricc constant of specimens sintered at 950 and 970, respectively. Curie temperature (T c ) of all the specimens was observed inn the vicinity of about 190. It was conformed that Tc with sintering temperature significantly unchanged. Figure 1. Temperature dependence of dielectric constant of PLZT ceramics. Figure 2 shows P-E hysteresis loops of PLZT ceramics with electric field at a range of temperature from 20 to 220. The specimen sintered at 950 showed the maximum values of E c =9.135 p C/N, P r =10.98 μc/cm 2. Coercive electric field (EE c ) and Remnant polarization (P r ) were decreased as a functionn of increasing temperature. In particular, as shown in figure 2, it can be seen that P-E hysteresis loops in the vicinity of 180 rapidly were slimed due to the phase transition from ferroelectric phase to paraelectricc phase was occurred at T c. 2

4 2015 Global Conference on Polymer and Composite Materials (PCM 2015) IOP Publishing IOP Conf. Series: Materials Science and Engineering 87 (2015) doi: / x/87/1/ Figurre 2. P-E hyysteresis loo ops of PLZT T ceramics as a function n of electric fields at diffferent temperature (a=950, b=970 0 ). LZT ceramics as a functiion of tempeerature Figurre 3. The poolarization veersus Tempeerature of PL changge under appplied electric fields (a=9550, b=970 ). Figurre 3 presents the changess in polarizattion with tem mperature und der applied eelectric field ds. As can be seen figure 3, the t remnant polarizationn decreased with increaasing tempeerature. In particular, p decreasee at range of o temperatu ure from 1000 to 220 is largerr than that aat range of different temperatture. These results show w that the phhase transitio on was occu urred from fferroelectric phase to paraelecttric phase at Tc. Figurre 4 shows temperature t variation ( T T) with tem mperature und der applied eelectric field ds. In this work, thhe EC effectt of PLZT ceramics waas measured d by indirectt method, annd T calcu ulated by Maxwelll s relation. (2) Heat capacity off specimens is approxim mately constaant for ferro oelectric cera ramics at x 106 (J/m3K). 50 showed d the maxim mum value off ~0.19 As shhown in figuure 4, T of ceramic ssintered at 95 under appplication off 30kV/cm at a 190, whhile ceramicss sintered at 970 exhibbited the tem mperature variationn of ~0.15. As a resultt, the maxim mum value off T was attrributed to thhe increase of entropy 3

5 because of T c. the phase transition from ferroelectric phase to paraelectric phase p was occurred in the vicinity Figure 4. Temperature variation ( T) of PLZT ceramics as a function of temperature under applied electricc fields (a=950, b=970 ). 4. Conclusions In this study, the electrocaloricc effects of f (Pb 0.88 La 0.0 8)(Zr 0.65 Ti )O 3 ferroelectric ceramics were investigated and discussed. Curie temperature (T c ) of PLZT ceramics was observed in the vicinity of 190. Coercive electric field (E c ) and Remnant polarization (Pr) weree rapidly decreased at Tc. Due to the phase transition from ferroelectric phase to paraelectric phase. Temperature variation ( T) was calculated by Maxwell s relations. T of ceramic sintered at 950 showed the maximum value of ~0.19 with application of 30 kv/cm at 190. References [1] Xiao D Q, Wang Y C, Zhang R L, Peng S Q, Zhu J G and Yang B 1998 Mater. Chem. Phys [2] Bai Y, Zheng G P, Ding K,, Qiao L, Shii S Q and Guo D 2011 J. Appl. Phys [3] Rožič B, Kosec M, Ursic H, Holc J, Malič B, Zhang Q M, Blinc R, Pirc R and Kutnjak Z 2011 J. Appl. Phys [4] Zheng X C, Zheng G P, Lin Z and Jangg Z Y 2012 J. Electroceram [5] Bai Y, Zheng G P and Shi S Q 2011 Mater. Res. Bull [6] Rožič B, Zhang Q M, Kutnjak Z, Li X, Furman E, Gorny L J, Lin M, Malič B, Kosec M, Blinc R, Pirc R Appl. Phys. Lett [7] Maiwa H and Kim S H 2013 Ceram. Int. 39 S497-S500 [8] Wang J, Yang T, Chen S, Li G, Zhang Q and Yao X 2013 J. Alloys Compd [9] Singh G, Tiwari V S 2012 J. Alloys. Compd [10] Saranya D, Chaudhuri A R, Parui J andd Krupanidhii S B 2009 Bull. B Mater. Sci