同步辐射-研究生组会presentation课件.ppt

1、 Synchrotron radiation topography study of temperature-induced phase transformation in unpoled 0.92Pb(Zn1/3Nb2/3)O30.08PbTiO3 crystals内容提要铁电材料简介1同步辐射在铁电材料上的应用2结 语3铁电材料简介铁电材料简介n铁电材料是一类特殊的电介质材料。它的主要特性是具有自发极化和电滞回线。n如图所示，在电场强度E变化过程中，极化强度P滞后于电场强度E,这种状况产生的回线，称为电滞回线。电滞回线产生原因n铁电晶体是由许多小区域(电畴)所组成，每个电畴内的极化方向一致

2、，而相邻电畴的极化方向则不同。从宏观来看，整个晶体是非极化的，呈中性 在外电场作用下，极化沿电场 方向的电畴扩大。电畴结构与 晶体结构有关常用铁电材料及应用n 研究最早,已广泛使用的包括钛酸钡BaTiO3（BT）、锆钛酸铅（(Pb(Zr1-xTix)O3）。n常用的铁电材料有铌锌酸铅（(Pb(Zn1/3Nb2/3)O3）铌镁酸铅（(Pb(Zn1/3Mg2/3)O3）或铌铁酸铅（(Pb(Fe1/2Nb1/2)O3）(PFN)和钛酸铅(PbTiO3)组成的具有钙钛矿结构的弛豫铁电材料(简称PZNT,PMNT和PFNT)。n铁电材料已应用于制造光滤波器、集成光器件、微电子机械系统、微处理器等。弛豫型

3、铁电体n本文研究的材料为0.92Pb(Zn1/3Nb2/3)O30.08PbTiO3，属于弛豫型铁电体。n弛豫型铁电体与普通铁电体主要的区别是具有不同的相变特性，即具有独特的弛豫特性，包括弥散性铁电相变特征和频率色散特征，而这些弛豫特性则起源于该类材料所特有的微观结构特征。主要内容abstractnThrough real time synchrotron radiation topography observation,dynamical behavior of ferroelectric domains as a function of temperature in unpoled PZN

4、8%PT crystals is investigated.A sequence of temperature-induced monoclinic phase transformations is observed,and verified by combining this method with temperature-dependence Raman scattering,capacitance measurement,and X-ray diffraction.This phase evolution picture seems remarkably unique as the mo

5、noclinic phase is able to coexist with the cubic phase well above TC.IntroductionnRelaxor ferroelectrics such as Pb(Zn1/3Nb2/3)O3 PbTiO3(PZNPT)and Pb(Mg1/3Nb2/3)O3PbTiO3(PMNPT)crys-tals,have been considered as a new generation of piezoelectric materials,due to their extremely excellent piezo-ferroel

6、ectric and electrostriction properties superior to those of the traditional PZT ceramics.Images of the in situ synchrotron radiation topography in PZN8%PT crystals,the x-rays incident direction to the crystal is 001,the diffraction vector is(112):(a)room temperature(b)heating to 75 C;(c)heating to 1

7、31 C;(d)heating to 132 C;(e)heating to 190 C;(f)heating to 262 C;(g)cooling to 190 C;(h)cooling to 75 C;(i)cooling to room temperature;(j)Schematic picture for presenting the ferroelectric domain configurations in the topography images of PZN8%PT crystals;(k)enlarged images of C domain walls from 75

8、 C to 190 C.The A domain walls,which are at approximately 45 to the 100 axis,can be obviously observed at room temperature.These domain walls are considered to be the 71 (or 109)ones in rhombohedral PZNPT crystals,and can be clearly observed before heating the sample to 132 C.With increasing tempera

9、ture from 75 C to 131 C,as shown in Fig.1(b)(c),the B domain laminates become progressively obvious and coexist with the A domains.A畴位于形貌图的左上部分，畴壁取向大约与晶体的010（或100轴）成45角;B畴位于形貌图的右上部分，畴壁取向平行于010轴;At the point of 131 C,the tetragonal domains become most clear.With heating the sample to above 132 C,as s

10、hown in Fig.1(d),we find that the rhombohedral 71 (or 109)domain walls(A laminates)become vague,and the image background becomes brighter than before.However,the tetragonal domain walls are still clear.This phenomenon shows that the phase transition from rhombohedral to tetragonal phase(RT transitio

11、n)starts at 75 C,and the tetragonal domains grow gradually.With further heating of the system to about 132 C,we find this domain structure is very stable and coexists with B tetragonal domains.Upon further heating to above Tc(170 C),the monoclinic C domain structure also remains.This case shows that

12、 a monoclinic phase not only appears in the process of ferroelectricferroelectric phase transformation,but also coexists with the cubic phase well above TC.With the temperature elevating to about 262 C,we find nearly all the ferroelectric domains disappear,as shown in Fig.1(f).The capacitancetempera

13、ture curve(C T curve)of PZN0.08PT crystal at 100 kHz.Fig.shows the capacitancetemperature curve(C T curve)at 100 kHz.Since the capacitance is directly proportion to the dielectric constant,the curve implies the evolution of the dielectric constant with respect to temperature.One small capacity peak

14、appears with the temperature elevating to 75 C and about 132 C,as shown in the figure.This capacitance anomaly shows a phase transformation at these two temperatures.We also find there appears a maximum Capacity peak near 170 C,which clarifies the Tc is about 170 C.Initially,we consider the Tc is ab

15、out 260 C according to that observed by the topography experiments.Most particularly,a set of unique domain walls(C domain walls)appear at this temperature,which is quite different from the A and B domains.This kind of domain walls is shown in Fig.1(k),through the enlarged images taken from 75 C to

16、190 C.As the figures show,the C domain laminates deviate from the 010 direction at 15 20.According to the knowledge of domains orientation in crystals with different symmetry and X-ray diffraction extinction relations,these laminates can be considered to be neither rhombohedral nor tetragonal domain

17、 structures,but a new monoclinic phase domain structureConclusionnThrough in situ synchrotron radiation topography under various temperatures,the complex configuration and dynamic evolution of ferroelectric domains in PZN8%PT crystals are obtained.Combining this technique with Raman scattering,ca-pa

18、citance measurement,and XRD experiment,a unique pic-ture of temperature-dependence phase transition sequence in PZN0.08PT crystals is revealed.结 语n关于同步辐射在铁电材料上的应用还有很多，例如铁电体的高压衍射，利用xfas进行微区成分涨落的探究，由于篇幅的问题，本文未涉及到。n本文采用的同步辐射光源是北京同步辐射国家实验室白光形貌站，进行白光X射线形貌研究。4W1A束线是主要用于X光形貌学及衍射研究的白光束线。该束线全长43 m，最大水平接收角为1.0 mrad，最大垂直接收角为4.3 mrad。多有不足，欢迎各位指正