Preparation and characterization of PMN-PT nanocomposite

Transcription

1 Indian Jurnal f Engineering & Materials Sciences Vl. 15, April 2008, pp Preparatin and characterizatin f PMN-PT nancmpsite Shrabanee Sen*, S K Mishra, S Sagar & S K Das MST Divisin, Natinal Metallurgical Labratry, Jamshedpur , India Received 10 Nvember 2006; accepted 28 February 2008 Ferrelectric ceramic-plymer cmpsites are cnsidered as prmising materials fr applicatins in sensrs, actuatrs and hydrphnes. They are attractive fr applicatin as they exhibit high piezelectric and pyrelectric respnse, lw acustic impedance matching with water and human skin and their prperties can be tailred t varius requirements. The advantage f cmpsites ver cnventinal ceramics is that they have better mechanical shck resistance and mre durable. Lead magnesium nibate-lead titanate (PMN-PT with 35 ml% PT) ceramic pwder is fabricated by citrate gel methd. The calcinatins temperature is ptimized by thermal analysis. The frmatin f the ceramic pwder is cnfirmed by XRD. The micrstructural prperties have been studied by, SEM and TEM. The particle size calculated frm TEM was fund t be between nm and the hmgeneus distributin f the pwders was als bserved. The cmpsites have been prepared using slvent casting in which the pwder is dispersed hmgeneusly in the plymer matrix. Different cmpsites are made by varying the ceramic t plymer rati. The structural, micrstructural prperties f the cmpsite are studied. Ferrelectric ceramic-plymer cmpsites are cnsidered as prmising materials fr applicatins in high-pressure sensrs, hydrphnes and actuatrs 1-3. The advantage f cmpsites ver cnventinal ceramics is that they have better mechanical shck resistance and mre durable. Reprted wrk n PZT- PVDF cmpsites f 0-3 cnnectivity prepared by bth slvent cast technique and ht press technique shwed that the results btained frm the cmpsites prepared by the ht press technique exhibited better sensivity, reprducibility and durability 4,5. Nwadays lead magnesium nibate-lead titanate (PMN-PT) with high piezelectric prperties has been widely studied 6,7. PMN-PT is the slid slutin f relaxr ferrelectric lead magnesium nibate (PMN) and nrmal ferrelectric lead titante (PT). It is fund that with 35% PT, it is near t the mrphtrpic phase bundary (MPB) regin and here the dielectric and piezelectric prperties are maximized because f the energy states f rhmbhedral and tetragnal structures. At this regin the utstanding piezelectric prperties have wide applicatins in transducers and actuatrs 8,9. PVDF is a cmmnly used ferrelectric plymer, which pssess gd piez and pyr prperties 9,10. This paper reprts study n the 0-3 cnnectivity f PMN-PT- PVDF cmpsites in different mlar rati (30,50, 70). The structural and micrstructural prperties f the prepared cmpsites have been studied. *Fr crrespndence ( shrabaneesen@yah.c.in) Experimental Prcedure The ceramic pwder (PMN-PT) was synthesized by the citrate-gel methd using misture insensitive and inexpensive precursrs like citrate salts (Ti and Nb) and nitrates (Pb and Mg). The citrate gel methd was preferred because the hmgenus mixing f the precursr slutin takes place and the calcinatins temperature is lwered which prevents lead lss. The details f the prcedure fr synthesis f ultra fine PMN-PT pwders are described belw: Preparatin f nibium and titanium citrate slutins Aqueus slutin f nibium citrate cmplex was prepared staring frm the xide (Nb 2 O 5 ), which was disslved in HF (>7 M) by warming the mixture ver water bath fr 2 days t btain a clear slutin f nibium-fluride cmplex (i.e NbF 5 2- cmplex). The hydrus nibium xide (Nb 2 O 5.nH 2 O) was precipitated ut frm the clear slutin f the nibium cmplex by additin f aqueus slutin f ammnia. The precipitate was washed with 5% ammnia slutin t make it fluride free. Finally, the precipitate was disslved in aqueus slutin f citric acid (2 M per unit ml f nibium in) with cntinuus stirring t btain a clear, aqueus slutin f nibium citrate. The slutin was assayed at 1000 C fr 2 h t estimate the amunt f nibium xide. Similarly titanium citrate slutin was made by disslving titanium xide (TiO 2 ) in HF slutin and further prcessing in the same way.

2 112 INDIAN J ENG. MATER. SCI., APRIL 2008 Preparatin f gel Required amunt f magnesium carbnate was taken and disslved in minimum amunt f nitric acid and t this slutin required amunt f lead nitrate was added. Further citric acid was added t in the mlar rati f 1:1. Prprtinate amunt f titanium and nibium citrate was taken and bth the slutin were mixed well. Ethylene glycl was added t the slutin in the rati f 0.25 M with respect t the ttal citrate ins. A white precipitate was frmed and ammnium citrate slutin was added t it in rder t maintain a ph value f 6. The clear slutin was heated at water bath fr 6 h, which resulted in the frmatin f a semi slid gel. The frmatin f the gel takes place due t the esterficatin f ethylene glycl and citric acid. This semi slid gel was heated vernight in an ven at 150P PC t get a hard gel, which was crushed and calcined at the ptimum temperature. Thermal analysis f the hard gel was dne t ptimize the calcinatins temperature. The gel was calcined at 600P PC fr 4 h t frm ultrafine pwders. XRD, SEM and TEM f the fine pwders were dne t study the structural and micrstructural prperties. Cmpsites f different mlar ratis (30, 50 and 70) in the 0 3 cnnectivity were prepared by ht press technique. The required amunt f plymer (PVDF) was taken and disslved in methyl ethyl ketne t frm a slutin. After hmgeneus mixing f the plymer in the slvent was cmpleted, the ceramic pwder was added t it slwly. The slutin was cntinuusly stirred well by a magnetic stirrer. After hmgeneity was achieved, the slutin was heated at 60P PC alng with cntinuus stirring. This cntinued till a gel like frmatin takes place and then the gel was pressed between tw metal discs. As the sample was pressed, the disk was heated up t 150P PC. Finally cmpsites n 1 2 mm were frmed. The prepared cmpsites were characterized by XRD, SEM and AFM. Results and Discussin Thermal analysis (Mdel DT-40, Shimadzu C, Japan) was carried ut in static air at a heating rate f 10P PC/min upt 1000P PC in rder t ptimize the calcinatin temperature. The TGA and DTA curves are shwn in Fig 1. The weight lss ccurred in tw steps, first an initial weight lss which resulted frm the evapratin f the absrbed water and then a rapid reductin up t 533P PC after which the mass lss saturates. Abve this temperature the TG curves shw n weight lss. This was als cnfirmed frm DTA curves, which shws tw exthermic peaks at 327P PC and 474P PC respectively. The strng exthermic peak indicates the release f a high amunt f heat due t cmbustin f the charred mass btained frm the decmpsitin f the metal citrate-ethylene glycl cmplex. It is als bserved that abve 550P PC n significant thermal effect was bserved in the DTA curve, which implies that cmplete ultrafine pwders. The phase frmatin f the pwder was cnfirmed by XRD (Fig. 2). XRD spectra revealed that the frmatin f the desired phase has taken place with a small amunt f pyrchlre phase (PbB2.31BNbB2BOB7B and PbNbB2BOB6B) marked in the figure. The particle mrphlgy, size and distributin was f the particles was studied by high-reslutin transmissin micrscpe (JEOL-JSM 2010 Electrn Micrscpe). Figure 3a shws the distributin f the particles and als depicts that the particle shape is nnspherical [Fig. 3b]. After statistic analysis the average particle size was fund t be 55±2 nm. Fig. 1 TGA and DTA pattern f PMN-PT nancmpsite. Fig. 2 Wide angle X-ray diffractin pattern f PMN-PT nancmpsite.

3 SEN et al.: PREPARATION AND CHARACTERIZATION OF PMN-PT NANOCOMPOSITE 113 This is in agreement with the particle size calculated frm diffractin peak. The crrespnding selected area electrn diffractin pattern f the same sample (Fig. 3c shws symmetrically dtted pattern, implying that the nanparticles are well crystallized. The HRTEM pattern f the selected area indicates that there are very similar rientatins in the particle (Fig. 3d). The lattice spacing in the particle was fund t be 2.3 Å, which was cmparable with the value Fig. 3a TEM f PMN-PT nancmpsite. Fig. 3d HRTEM image f PMN-PT nancmpsite. Fig.3b TEM f PMN-PT nancmpsite frm a different regin. Fig. 4 Istherm reveals that is f Type I in IUPAC system, which indicates the frmatin f nn-prus material. Fig. 3c Selected area diffractin pattern f PMN-PT. Fig. 5 XRD pattern fr different cncentratin f PMN-PT.

4 purge 114 INDIAN J ENG. MATER. SCI., APRIL 2008 btained frm XRD analysis. The surface area f the fine pwder was measured by the Brunauer-Emmet-Teller (BET) methd in a Beckman Cunter Analyzer (Miami, FL). Befre NB2B adsrptin- desrptin measurement, each sample was degassed with a NB2B at 77 K fr 3 h. The 2-1 specific surface area was fund t be 68 mp P/gP P. The istherm shwn in Fig. 4 reveals that is f Type I in IUPAC system, which indicates the frmatin f nnprus material. The characterizatin f the prepared cmpsites was dne by XRD, SEM and AFM. Figure 5 shws the rm temperature XRD pattern f the cmpsites using CKBαB target. The first ne shws the diffractin pattern f PVDF plymer. The amrphrus nature f the plymer is mre prminent there. The next three graphs shw the diffractin pattern f the cmpsites in different ratis, i.e., 10, 30 and 50%. Fr the lwest cncentratin ne peak f PVDF is visible. The diffractin peaks are mre r less same with change in Fig. 6 SEM micrgraphs f the cmpsite PMN-PT-PVDF 10% at (a) 500 and (b)1000 magnificatin. Fig. 7a Tpgraphic images f PVDF using atmic frce micrscpy (AFM). Fig. 7 (b-d) AFM f the cmpsite PMN-PT and PVDF.

5 SEN et al.: PREPARATION AND CHARACTERIZATION OF PMN-PT NANOCOMPOSITE 115 intensity r Bragg angle value. This is due t the change in the rati f the plymer and the ceramic. A rugh estimatin f the particle size was dne using Scherer s equatin and it was fund t be 22, 24 and 28 nm respectively fr 10, 30 and 50% rati f ceramic t plymer. The pattern suggests gd crystallinity and the interactin f the ceramic with the plymer is als visible. Figures 6a and 6b shw the SEM micrgraphs f the cmpsite PMN-PT-PVDF 10%. In Fig. 6a the plymer matrix is clearly visible with sme ceramic pwders embedded inside it. Further with higher magnificatin (Fig. 6b) the ceramic pwders within the plymer matrix is mre prminently seen. Tpgraphic images f the cmpsites were taken by atmic frce micrscpy (AFM). The first figure (Fig. 7a) shws the hmgeneus distributin f the plymer (PVDF) in the slvent. It als indicates the single-phase cmpnent f the plymer nly. The ther three figures (Figs 7b-7d] shw the presence f tw phases dented by light and dark gray regin. The increase in the ceramic t plymer rati is als clearly evident frm the micrgraphs. In Fig. 7d the distributin f the ceramic pwders is unifrm thrughut the plymer matrix as the rati between them is 50%. Cnclusins PMN-PT ultrafine pwders were prepared by citrate gel methd. The frmatin f the cmpund was cnfirmed by XRD analysis. The crystallite size was fund t be 50 nm which was cmparable with that btained frm TEM micrgraphs, i.e., 55 nm. The cmpsites were prepared by taking different ratis f plymer (PVDF) and the ceramic pwders by ht press technique. AFM micrgraphs shw the well distributin and rati f the ceramic t plymer matrix in the cmpsite. References 1 Skinner D P, PhD Thesis, Lubitz K, Wlff A & Peru G, Ferrelectrics, 133 (1992) Shrut T R & Schulze W A, Mater Res Bull, 14 (1979) Satish B, Sridevi K & Vijaya MS, J Phys D: Appl Phys, 35 (2002) Venkatragavaraj E, Satish B, Vind P R & Vijaya MS, J Phys D: Appl Phys, 34 (2001) Chy S W & Shrut T R, Ferrelectrics, Shrut T R, Chang Z P, Kim N & Markgarf S, Ferr Lett, 12 (1990) Tressler J F & Hwarth T R, Prc 2 th IEEE Int Symp, 2 (2000) Chen H L W, Ng P K L, Chy C L, Appl Phys Lett, 74 (1999) Swartz S L & Shrut T R, Mater Res Bull, 17 (1982) 1245.