準(zhǔn)同型相界鈦酸鉍鈉基鐵電固溶體的電卡效應(yīng)研究

唐　瑾, 王飛飛, 李　巖, 田承越, 汪　青, 石旺舟

(上海師范大學(xué) 數(shù)理學(xué)院,上海 200234)

準(zhǔn)同型相界鈦酸鉍鈉基鐵電固溶體的電卡效應(yīng)研究

唐瑾, 王飛飛, 李巖, 田承越, 汪青, 石旺舟

(上海師范大學(xué) 數(shù)理學(xué)院,上海 200234)

摘要:利用鐵電材料的電卡效應(yīng)實現(xiàn)致冷成為當(dāng)前國內(nèi)外的研究熱點之一.基于Maxwell 關(guān)系,圍繞著準(zhǔn)同型相界組分的Bi0.5Na0.5TiO3基無鉛鐵電固溶體,研究了其電卡效應(yīng),結(jié)果表明:該體系在5 kV/mm的外電場下,顯示出優(yōu)異的致冷特性,溫度的變化量可達(dá)到1.15 K,相應(yīng)的致冷強(qiáng)度可達(dá)0.23 K·mm/kV,在全新的固態(tài)致冷器件中顯示出應(yīng)用前景.

關(guān)鍵詞:電卡; 無鉛; 鐵電致冷; 準(zhǔn)同型相界

0引言

電卡效應(yīng)是熱釋電效應(yīng)的逆效應(yīng),它是指在極性材料中由于外加電場的改變從而引起系統(tǒng)的極化狀態(tài)的變化,從而產(chǎn)生絕熱溫變或等溫熵變[1].電卡效應(yīng)提供了一種全新的固態(tài)制冷的方法,與傳統(tǒng)的壓縮致冷方法相比,鐵電致冷具有高效率、環(huán)保、健康等優(yōu)點;與磁致冷相比較,外電場的調(diào)控更加容易,有利于設(shè)計及器件的小型化,因此近來受到國內(nèi)外研究人員的廣泛關(guān)注,在一些固態(tài)的設(shè)備制冷上有著非常重要的應(yīng)用前景[2].

電卡效應(yīng)的研究最早可以追溯到1930年,Kobeco 和 Kurtschatov在羅息鹽中發(fā)現(xiàn)了電卡效應(yīng)[3].但在當(dāng)時由于效應(yīng)比較弱,沒有進(jìn)行定量表征,直到1956年才首次報道了SrTiO3具體的數(shù)值[4].1960~1970年左右,掀起了電卡效應(yīng)的研究熱潮,但是由于鐵電材料性能的限制,電卡效應(yīng)都相對較弱,測得的絕熱溫變大都在1 K以下.2006年,國際上Mischenko等人率先在PbZr0.95Ti0.05O3(PZT) 薄膜中報道了較大的絕熱溫變,在居里溫度附近,電卡效應(yīng)達(dá)到0.48 K/V[5].隨后,圍繞薄膜體系的電卡效應(yīng)的研究取得了進(jìn)一步突破,溫變可達(dá)到十幾K[6-8].

1實驗

采用傳統(tǒng)的固相燒結(jié)方法,制備了準(zhǔn)同型相界組分Mn改性的0.895 Bi0.5Na.5TiO3-0.04Bi0.5K0.5TiO0.3-0.065BaTiO3(BNKBMT) 陶瓷,具體過程可參考本文作者前期研究工作[18].利用X射線衍射儀 (D8 Focus,Bruker,Germany) 對樣品的結(jié)構(gòu)進(jìn)行分析,利用阻抗分析儀 (Agilent HP4294A,Santa Clara,CA) 測試樣品的介電性能,采用鐵電分析儀(TF2000 analyzer,Aixacct,Aachen,Germany)測試了不同溫度的電滯回線,采用DSC (DSC-2C,Perkin Elmer,America)測試了樣品的熱容.

2結(jié)果與討論

根據(jù)XRD結(jié)果,從慢掃的 (111) 和 (200) 兩個特征衍射峰(分別對應(yīng)三方相與四方相)中可以看出,BNKBMT陶瓷處于準(zhǔn)同型相界組分,室溫下鐵電三方相和四方相共存[18].圖1(a) 是BNKBMT陶瓷極化后的介電常數(shù)和損耗隨溫度的變化曲線,測試溫度為25~400℃,測試頻率為100 Hz~100 kHz.從圖1(a) 可以看出,樣品具有較寬的介電峰,顯示出典型的彌散性相變過程,并且有兩個特征溫度,一個對應(yīng)退極化溫度Td,通常由介電損耗的峰值溫度來確定,另一個是介電常數(shù)的峰值溫度Tm.圖1(a)表明,對于極化后的樣品,當(dāng)溫度低于Td時,介電常數(shù)幾乎不隨測試頻率的變化而變化,表明在外加電場的作用下,鐵電微疇結(jié)構(gòu)轉(zhuǎn)化為宏疇結(jié)構(gòu).當(dāng)溫度超過Td時,因為溫度擾動使得鐵電宏疇結(jié)構(gòu)被破壞,介電常數(shù)顯示出強(qiáng)的色散現(xiàn)象.Tm附近有很寬的介電峰,表明了BNKBMT的彌散性相變特征,這主要是因為體系中A位有多種離子(Bi3+,Na+,Ba2+,K+) 存在,引起微區(qū)間成分的不均勻而造成的[18].

圖1(b) 是BNKBMT不同溫度下的電滯回線,測試電場 5 kV/mm,頻率為10 Hz.從圖1(b)中可以看出,隨著溫度不斷升高,剩余極化和矯頑場均不斷減小,當(dāng)溫度接近退極化溫度 (70 ℃) 時,電滯回線呈現(xiàn)明顯的雙電滯回線的特點.對出現(xiàn)雙電滯回線的原因,早期認(rèn)為是由于陶瓷從三方鐵電相到反鐵電相的相變引起的,但目前仍然存在爭議,沒有有力的證據(jù)報道.當(dāng)溫度超過180 ℃,電滯回線表現(xiàn)一般電介質(zhì)的響應(yīng).

(1)

圖1(d) 為計算得到的不同電場下BNKBMT陶瓷的ΔT隨溫度的變化關(guān)系.從圖1(d)中可以看出,與介溫頻譜相似,相應(yīng)的ΔT隨溫度增加也呈現(xiàn)寬的峰,對應(yīng)的峰值溫度位于Td附近(100 ℃ @ 1 kV/mm).隨著電場的增加,ΔT的峰值不斷增大,這是由于在高電場下,BNKBMT的有序程度增加,相應(yīng)的熵減少的緣故.在5 kV/mm的電場下,ΔT的最大值可達(dá)到1.15 K.

表1小結(jié)了近期報道的相關(guān)鐵電單晶、陶瓷體系的電卡效應(yīng),從表1中可以看出,與其他無鉛體系相比,準(zhǔn)同型相界BNKBMT體系呈現(xiàn)較高的電卡強(qiáng)度,達(dá)到0.23 K·mm/kV,與鉛基體系也相接近,顯示了BNKBMT在制冷器件應(yīng)用中具有一定的優(yōu)勢.

3結(jié)論

本研究利用Maxwell關(guān)系研究了準(zhǔn)同型相界組分BNKBMT陶瓷的電卡效應(yīng),結(jié)果表明,在退極化溫度附近,具有最大電卡效應(yīng),5 kV/mm的電場下,ΔTmax值達(dá)到1.15 K,相應(yīng)的致冷強(qiáng)度可達(dá)0.23 K·mm/kV,在新型環(huán)境友好的鐵電制冷器件中顯示出一定的應(yīng)用前景.

參考文獻(xiàn):

[1]SCOTT J F.Electrocaloric materials[J].Annual Review of Materials Research,2011,41:229-240.

[2]LU S G,TANG X G,WU S H.Large electrocaloric effect in ferroelectric materials[J].Journal of Inorganic Materials,2014,29(1):06-07.

[3]KOBECO P,KURTCHATOV I V.Dielectric properties of rochelle salt crystal[J].Zeitschrift für Physikalische,1930,66:192-205.

[5]MISCHENKO A S,ZHANG Q,SCOTT J F,et al.Giant electrocaloric effect in thin-film PbZr0.95Ti0.05O3[J].Science,2006,311(5765):1270-1271.

[6]FENG Z,SHI D,DOU S.Large electrocaloric effect in highly (001)-oriented 0.67PbMg1/3Nb2/3O3-0.33PbTiO3thin films[J].Solid State Communications,2011,151(2):123-126.

[7]FENG Z,SHI D,ZENG R,et al.Large electrocaloric effect of highly (100)-oriented 0.68PbMg1/3Nb2/3O3-0.32PbTiO3thin films with a Pb(Zr0.3Ti0.7)O3/PbOxbuffer layer[J].Thin Solid Films,2011,519(16):5433-5436.

[8]CHEN H,REN T L,WU X M,et al.Giant electrocaloric effect in lead-free thin film of strontium bismuth tantalite[J].Applied Physics Letters,2009,94(18):182902.

[10]VALANT M,DUNNE L J,AXELSSON A K,et al.Electrocaloric effect in a ferroelectric Pb(Zn1/3Nb2/3)O3-PbTiO3single crystal[J].Physical Review B,2010,81(21):214110.

[11]GOUPIL F L,BERENOV A,AXELSSON A K,et al.Direct and indirect electrocaloric measurements on (001)-PbMg1/3Nb2/3O3-30PbTiO3single crystals[J].Applied Physics Letters,2012,111(12):124109.

[12]HAGBERG J,UUSIMKi A,JANTUNEN H.Electrocaloric characteristics in reactive sintered 0.87Pb(Mg1/3Nb2/3)O3-0.13PbTiO3[J].Applied Physics Letters,2008,92:132909.

[13]BAI Y,HAN X,QIAO L J.Optimized electrocaloric refrigeration capacity in lead-free (1-x)BaZr0.02Ti0.08O3-xBa0.7Ca0.3TiO3ceramics[J].Applied Physics Letters,2013,102(25):252904.

[14]Directive 2002/95/EC,On the restriction of the use of certain hazardous substances in electrical and electronic equipment[S].European Union:Official Jounal of the European Communities,2003.

[15]TAKENAKA T,NAGATA H.Current status and prospect of lead-free piezoelectric ceramics[J].Journal of the European Ceramic Society,2005,25(12):2693-2700.

[16]SUN R,ZHANG Q,FANG B,et al.Dielectric,electromechanical coupling properties of Mn-doped Bi0.5Na0.5TiO3-BaTiO3lead-free single crystal[J].Applied Physics A,2011,103(1):199-205.

[17]ZHANG Q H,ZHANG Y Y,WANG F F,et al.Enhanced piezoelectric and ferroelectric properties in Mn-doped Bi0.5Na0.5TiO3-BaTiO3single crystals[J].Applied Physics Letters,2009,95(10):102904.

[18]XU M,WANG F F,WANG T,et al.Phase diagram and electric properties of the (Mn,K)-modified Bi0.5Na0.5TiO3-BaTiO3lead-free ceramics[J].Journal of Materials Science,2011,46(13):4675-4682.

[19]BAI Y,ZHENG G P,SHI S Q,et al.Abnormal electro caloric effect of Bi0.5Na0.5TiO3-BaTiO3lead-free ferroelectric ceramics above room temperature[J].Materials Research Bulletin,2011,46:1866-1869.

[20]TANG J,WANG F F,SHI W Z.Influence of the composition-induced structure evolution on the electrocaloric effect in Bi0.5Na0.5TiO3-basedsolid solution[J].Ceramies International,2015,41:3888-3893.

[21]LIU X Q,CHEN T T,WU Y J,et al.Enhanced electrocaloric effects in spark plasma-sintered Ba0.65Sr0.35TiO3-based ceramics at room temperature[J].Journal of the American Ceramic Society,2013,96(4):1021-1023.

[22]BAI Y,HAN X,DING K,et al.Combined effects of diffuse phase transition and microstructure on the electro caloric effect in Ba1-xSrxTiO3ceramics[J].Applied Physics Letters,2013,103(16):162902.

[23]WANG J F,YANG T Q,CHEN S C,et al.Nonadiabatic direct measurement electro caloric effect in lead-free Ba,Ca(Zr,Ti)O3[J].Journal of Alloys and Compounds,2013,550:561-563.

[24]LUO L H,CHEN H B,ZHU Y J,et al.Pyroelectric and electrocaloric effect of (111) oriented 0.9PMN-0.1PT single crystal[J].Journal of Alloys and Compounds,2011,509(32):8149-8152.

[25]WANG J F,YANG T Q,WEI K,et al.Temperature-electric field hysteresis loop of electrocaloric effect in ferroelectricity-direct measurement and analysis of electrocaloric effect.[J].Applied Physics Letters,2013,102(15):152907.

[26]SHEBANOVS L,BORMAN K,LAWLESS W N,et al.Electrocaloric effect in some perovskite ferroelectric ceramics and multilayer capacitors[J].Ferroelectrics,2002,273(1):137-142.

(責(zé)任編輯：顧浩然)

[27]LUO L H,DIETZE M,SOLTERBECK C H,et al.Orientation and phase transition dependence of the electrocaloric effect in 0.71PbMg1/3Nb2/3O3-0.29PbTiO3single crystal[J].Applied Physics Letters,2012,101(6):062907.Electrocaloric materials[J].Annual Review of Materials Research,2011,41:229-240.

The electrocaloric effect of Bi0.5Na0.5TiO3-based solid solution withthe composition around the morphotropic phase boundaryTANG Jin, WANG Feifei, LI Yan, TIAN Chengyue, WANG Qing, SHI Wangzhou

(College of Mathematics Science,Shanghai Normal University,Shanghai 200234,China)

Abstract:Recently,the electrocaloric effect of ferroelectric materials has attracted much attention at home and abroad due to its potential applications in solid-state refrigeration.In this paper,based on Maxwell relations,we study the electrocaloric effect of Bi0.5Na0.5TiO3-based lead-free ferroelectric quasi-solid solution with the composition focusing around the morphotropic phase boundary.The results show that the system has excellent refrigeration characteristics under external electric field of 5 kV/mm and the amount of change in temperature reaches 1.15 K.The corresponding refrigeration strength reaches 0.23 K·mm/kV,showing the prospect of applications in new environmental-friendly solid-state cooling devices.

Key words:electrocaloric effect; lead-free; ferroelectric refrigeration; morphotropic phase boundary

通信作者:王飛飛,中國上海市徐匯區(qū)桂林路100號,上海師范大學(xué)數(shù)理學(xué)院光電子材料與器件重點實驗室,郵編200234,E-mail:ffwang@shnu.edu.cn;石旺舟,中國上海市徐匯區(qū)桂林路100號,上海師范大學(xué)數(shù)理學(xué)院光電子材料與器件重點實驗室,郵編200234,E-mail:wzshi@shnu.edu.cn

基金項目:國家自然科學(xué)基金(11204179,61376010);上海市教委“晨光計劃”(11CG49)

收稿日期:2014-09-02

中圖分類號:TB 34

文獻(xiàn)標(biāo)志碼:A

文章編號:1000-5137(2015)02-0127-05