Chế tạo và nghiên cứu các tính chất vật lý của hệ vật liệu xBZT – (1 – x)BCT pha tạp

I HC HU TRNG I HC KHOA HC - NG ANH TUN CH TO V NGHIấN CU CC TNH CHT VT Lí CA H VT LIU xBZT (1 x )BCT PHA TP Chuyờn ngnh: Vt lý Cht rn Mó s: 62.44.01.04 TểM TT LUN N TIN S KHOA HC VT CHT Hu, 2016 Cụng trỡnh c hon thnh ti Trng i hc Khoa hc i hc Hu Ngi hng dn khoa hc TS Trng Vn Chng PGS TS Vừ Thanh Tựng Phn bin 1:GS TS Bch Thnh Cụng, Trng i hc Khoa hc T nhiờn HQG H Ni Phn bin 2: PGS TSKH Nguyn Th Khụi, Trng i hc S phm H Ni Phn bin 3: PGS TS Trng Minh c, Trng i hc S phm i hc Hu Lun ỏn s c bo v ti Hi ng chm lun ỏn cp i hc Hu hp ti: Vo lỳc gi ngy thỏng .nm Cú th tỡm hiu lun ỏn ti Th vin Quc gia H Ni Trung tõm hc liu - i hc Hu Th vin Trng i hc Khoa hc - i hc Hu M U PZT l cỏc vt liu cú tớnh st in, ỏp in mnh H s ỏp in d33 ca vt liu ó tng t 200 pC/N vt liu PZT khụng pha lờn 300 pC/N PZT4, 400 pC/N PZT-5A, v gn 600 pC/N PZT-5H Mc du vy, vt liu PZT cha chỡ, mt nguyờn t c hi nh hng n sc khe ngi v mụi trng sng ó cú rt nhiu h vt liu ỏp in khụng chỡ ó c quan tõm nghiờn cu Tuy nhiờn, cỏc gm ỏp in khụng chỡ u cú h s ỏp in thp so vi cỏc h gm PZT c chỳng cú thnh phn vt liu nm vựng biờn pha hỡnh thỏi hc (MPB) BaTiO3 vt liu ỏp in khụng chỡ ó c nghiờn cu t lõu Cỏc tớnh cht in ca BaTiO3 cú th c iu chnh thay th cỏc nguyờn t khỏc vo v trớ A hoc/v B mng ABO3 ca nú Nm 2009, Liu v Ren ó xõy dng c h vt liu BaZr0.2Ti0.8O3-xBa0.7Ca0.3TiO3 (BZT-BCT) cú h s ỏp in d33 t giỏ tr 620 pC/N x = 50%, cao hn c giỏ tr thu c trờn PZT5H Cỏc tỏc gi cũn nhn nh, h s ỏp in d33 ca thnh phn BZT-50BCT dng n tinh th hoc nh hng theo mt s phng tinh th xỏc nh (texture) cú th t giỏ tr 1500 pC/N õy l kt qu u tiờn cụng b trờn Tp Physical Review Letters B, mt thụng tin ỏng tin cy, thu hỳt s quan tõm ca cỏc nh cụng ngh vỡ kh nng ng dng ca chỳng (h s ỏp in v hng s in mụi ln, nhit chuyn pha st in - thun in nm gn nhit phũng) v cỏc nh nghiờn cu c bn vỡ ln u tiờn thu c ỏp in ln i vi vt liu ỏp in khụng chỡ MPB ca h vt liu ny tỏch riờng pha mt thoi v pha t giỏc c im quan trng nht ca h BZT-xBCT, khỏc vi cỏc h khụng chỡ cũn li, l s tn ti ca im ba, giao im gia pha mt thoi, t giỏc v lp phng S tn ti ca im ba ny c trng cho cỏc h vt liu PZT Sau phỏt hin ca Liu v cng s, cỏc vt liu tng t cng c ch to v cho cỏc thụng s khỏ tt vựng lõn cn MPB Cỏc kt qu ny cho phộp chỳng ta hy vng v kh nng ch to cỏc vt liu khụng cha chỡ cú tớnh ỏp in mnh mi tng quan vi vt liu cha chỡ Cỏc nghiờn cu c bn tỡm hiu c ch hỡnh thnh tớnh phõn cc in mụi ln h vt liu nhm nõng cao cỏc h s in, c cng nh ti u hoỏ cụng ngh ch to ang tr thnh thi s T nhng phõn tớch trờn, chỳng tụi chn ti cho lun ỏn l Ch to v nghiờn cu cỏc tớnh cht vt lý cah vt liu xBZT (1-x)BCT pha i tng nghiờn cu ca lun ỏn l h vt liu ỏp in cú dng tng quỏt xBZT-(1-x)BCT Ni dung nghiờn cu bao gm - Mt l, xõy dng quy trỡnh cụng ngh v ch to c h vt liu ỏp in khụng cha chỡ xBaZr0.2Ti0.8O3-(1-x)Ba0.7Ca0.3TiO3 pha tp; - Hai l, nghiờn cu cỏc tớnh cht st in, in mụi, ỏp in ca cỏc vt liu; - Ba l, nghiờn cu mt s tớnh cht vt lý ca vt liu bng phng phỏp phn t hu hn - Bn l, th nghim ng dng vt liu ch to bin t thy õm Phng phỏp nghiờn cu c s dng ch yu l phng phỏp thc nghim kt hp vi cỏc chng trỡnh phõn tớch, mụ phng nghiờn cu cỏc c trng ca vt liu, c th l Lun ỏn c thc hin l mt cụng trỡnh khoa hc u tiờn ti Vit Nam nghiờn cu mt cỏch h thng v cỏc tớnh cht vt lý ca cỏc h vt liu ỏp in khụng chỡ ti hng ti ch to mt h vt liu ỏp in thõn thin vi ngi v mụi trng cú cỏc thụng s ỏp in khỏ ln, tn hao in mụi thp ỏp ng c yờu cu mt s ng dng c th CHNG TNG QUAN Lí THUYT Chỳng tụi ó trỡnh by tng quan lý thuyt v cỏc tớnh cht in mụi, st in nh hng cho cỏc nghiờn cu v lý gii cỏc kt qu Cựng vi ú, cỏc c trng ca cỏc vt liu khụng chỡ núi chung, v vt liu trờn nn BaTiO3 núi riờng cng c gii thiu mt cỏch khỏi quỏt CHNG CC PHNG PHP NGHIấN CU V THC NGHIM TNG HP H VT LIU P IN xBaZr0.2Ti0.8O3-(1-x)Ba0.7Ca0.3TiO3 2.1 Cỏc phng phỏp nghiờn cu 2.1.1 Phõn tớch cu trỳc, vi cu trỳc v ỏnh giỏ cht lng mu Cu trỳc tinh th ca vt liu c phõn tớch thụng qua gin nhiu x tia X (D8-Advanced, BRUKER AXS) Cỏc tham s mng c tớnh toỏn bng phn mm PowderCell Hỡnh thỏi b mt ca vt liu c nghiờn cu bng nh SEM (thit b Nova NanoSEM 450-FEI) Phn mm ImageJ c s dng ỏnh giỏ c ht 2.1.2 Nghiờn cu tớnh cht in mụi Ngoi cỏc i lng c trng in mụi trng thỏi tnh, cỏc tớnh cht in mụi c nghiờn cu thụng qua phộp o s ph thuc ca in dung v gúc pha theo nhit (HIOKI 3235-50 LCR HiTESTER) Nu vt liu th hin tớnh cht chuyn pha nhũe, s ph thuc (T) tuõn theo cỏc nh lut Curie - Weiss m rng, Vogel Fulcher, v dng ton phng 2.1.3 Nghiờn cu c trng st in ca vt liu Hi ỏp P(E) hay ng tr st in c quan sỏt bi phng phỏp mch Sawyer Tower 2.1.4 Nghiờn cu tớnh cht ỏp in o 927.55 C o 709.17 C TG (mg) m (mg) - 3.74 -2 m (mg) - 1.478 -4 m (%) - 6.974 -6 0.0 -0.1 -0.2 -0.3 dTG (mg/min) Cỏc thụng s ỏp in c tớnh toỏn trờn c s phộp o cng hng (HP4193A, Agilent 4396B) v cỏc chun quc t v ỏp in 2.2 Quy trỡnh ch to h vt liu ỏp in xBZT-(1-x)BCT Vt liu ban u c chn l BaCO3, CaCO3, TiO2, ZrO2 (Mecrk, > 99%) Chỳng c phi liu theo hp thc xBaZr0.2Ti0.8O3-(1-x)Ba0.7Ca0.3TiO3, vi x = 0.42-0.56 l t l ca thnh phn BaZr0.2Ti0.8O3 Hn hp phi liu c nghin bng mỏy nghin hnh tinh Bt, sau nghin, c nung s b chn ỳng ch nhit to pha, chỳng tụi thc hin phõn tớch nhit TGADSC i vi thnh phn x = 0.48 0.1 200 400 m (%) - 17.643 600 800 1000 1200 T (oC) Hỡnh 2.8 Gin phõn tớch nhit TGA-DSC ca thnh phn x = 0.48 V nguyờn tc, nhit nung s b phi c chn lõn cn 927oC (im thu nhit th 2, hỡnh 2.8) Tuy nhiờn, lng hp thc dựng cho phộp phõn tớch nhit (21.2 mg) rt so vi lng vt liu cn ch to mu, vy, nhit nung phi c chn ln hn im thu nhit th hai c (250-300)oC, tc l khong 1250oC Chỳng tụi ó kho sỏt ph nhiu x tia X ca bt 0.48BZT c nung s b 1150oC, 1200oC, v 1250oC (hỡnh 2.9) 0.48BZT C-ờng độ (đvtđ) Thành phần khác 1250C 1200C 1150C 20 30 40 50 60 70 80 Hỡnh 2.9 Gin XRD ca bt 0.48BZT nung cỏc nhit T hỡnh 2.9, nhit nung s b 1250oC c chn l hp lý Bt, sau quỏ trỡnh nghin li 20 gi, c ộp thnh viờn dng a v thiờu kt cỏc nhit 1300oC, 1350oC, 1400oC, v 1450oC, gi Bng 2.5 Mt s i lng ỏp in ca thnh phn 0.48BZT theo nhit thiờu kt o T ( C) 1300 1350 1400 1450 1500 kp 0.16 0.31 0.49 0.52 0.50 kt 0.16 0.32 0.37 0.55 0.47 d31 (pC/N) -74 -157 -162 -188 -188 d33 (pC/N) 68 203 361 542 538 S liu bng 2.5 cho thy, cỏc h s liờn kt in - c v cỏc h s ỏp in u thay i tng nhit thiờu kt, v t giỏ tr ln nht ti 1450oC Kt qu ny cựng vi quy lut thay i ca tn hao in mụi l c s chn 1450oC lm nhit thiờu kt i vi thnh phn vt liu 0.48BZT CHNG MT S TNH CHT VT Lí CA H VT LIU xBZT-(1-x)BCT Chng ny trỡnh by mt s tớnh cht vt lý ca h vt liu xBZT (1 x)BCT thiờu kt 1450oC, vi x = 0.42-0.56 l t phn BZT h Ký hiu cỏc mu ng vi mi giỏ tr ca x l xBZT 3.1 Cu trỳc v hỡnh thỏi b mt ca vt liu Hỡnh 3.1 l gin XRD ca h vt liu xBZT ti nhit phũng C-ờng độ (đvtđ) (a) (b) 0.56BZT 0.56BZT 0.54BZT 0.54BZT (200)R 0.52BZT (200)R T (0 02 ) 0.48BZT )T 00 (2 0.50BZT (002)T(200)T 0.46BZT 0.44BZT 0.42BZT 20 30 40 50 60 () 70 80 0.52BZT 0.50BZT 0.48BZT 0.46BZT 0.44BZT 0.42BZT 44.0 44.5 45.0 45.5 46.0 46.5 () Hỡnh 3.1 Gin XRD ca h vt liu xBZT Hỡnh 3.1a cho thy, tt c cỏc mu u cú cu trỳc perovskite hon chnh Hỡnh 3.1b biu din gin XRD ca vt liu khong 44o-46o Khi x < 0.48, vt liu cú i xng t giỏc Khi x > 0.48, vt liu s hu i xng mt thoi Thnh phn x = 0.48 tn ti ng thi hai pha: T giỏc v mt thoi, ú, pha t giỏc chim 71.7% (hỡnh 3.3) Nh vy, MPB ca h cú th nm thnh phn 0.48BZT C-ờng độ (đvtđ) Tứ giác Mặt thoi o 0.52BZT 45.21 0.50BZT 45.21 0.48BZT 0.46BZT 44.7 o o 45.10 o 45.21 o 45.36 o 45.38 o 45.11 45.0 45.3 45.6 (o) 45.9 Tần suất Hỡnh 3.3 Gin XRD vựng 44o-46o ca mu 0.48BZT c lm khp vi hm Gauss Hỡnh 3.4, 3.5 l nh SEM v s phõn b c ht ca mu 0.48BZT c thiờu kt 1450oC 35 0.48BZT 30 Tần suất Đ-ờng làm khớp Gauss 25 20 15 10 0 10 20 30 40 50 60 70 80 Sg (àm) Hỡnh 3.4 nh SEM v s phõn b c ht ca vt liu 0.48BZT S phõn b c ht qua vic phõn tớch nh SEM ca vt liu bng phn mm ImageJ Bờn cnh ú, kớch thc ht trung bỡnh ca vt liu cng c tớnh toỏn bng chng trỡnh Lince (bng 3.2) Bng 3.2 Kớch thc ht trung bỡnh ca h vt liu xBZT Mu Kớch thc ht, Sg (àm) Phn mm Lince Phn mm ImageJ T trng, (kg/m3) 0.42BZT 22.6 22.5 5351 0.44BZT 24.1 22.0 5482 0.46BZT 28.4 25.2 5534 0.48BZT 32.4 29.2 5624 0.50BZT 30.0 25.5 5602 0.52BZT 26.4 23.5 5531 0.54BZT 27.9 27.0 5493 0.56BZT 24.8 23.2 5452 3.2 Tớnh cht in mụi Bng 3.3 thụng kờ hng s in mụi v tn hao in mụi iu kin tnh ca h vt liu xBZT Bng 3.3 Giỏ tr v tan ca vt liu xBZT iu kin tnh x 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 1054 2253 2406 3321 2808 2504 2404 2230 tan (%) 2.3 1.8 1.4 1.3 1.4 1.4 1.7 2.4 Nng BZT nh hng mnh n cỏc i lng in mụi ca vt liu Khi nng BZT tng, hng s in mụi v tn hao in mụi bin i ng thi, t giỏ tr cc i v cc tiu, tng ng ti thnh phn 0.48BZT 14000 r 12000 10000 8000 6000 4000 2000 25 50 0.42BZT 0.44BZT 0.46BZT 0.48BZT 0.50BZT 0.52BZT 0.54BZT 0.56BZT (a) i 500 (b) 400 300 200 100 75 100 125 T (oC) 25 50 75 100 125 T (oC) tan (c) 25 50 75 100 125 T (oC) Hỡnh 3.6 S ph thuc nhit ca (a) phn thc, r, (b) phn o, i, v (c) tn hao in mụi, tan ca vt liu xBZT Kt qu o in mụi theo nhit ti 1kHz trờn hỡnh 3.6 cho thy, s chuyn pha st in - thun in cú dng di rng õy l mt c trng ca vt liu st in relaxor nhũe ca vt liu c xỏc nh t dc ca ng lm khp s liu thc nghim vi dng bin i (3.3) ca nh lut Curie Weiss m rng ln 1 r r m ln T (3.3) Đ-ờng làm khớp -8 0.56BZT, = 1.664 0.54BZT, = 1.794 -10 0.52BZT, = 1.810 -12 0.50BZT, = 1.778 -14 0.48BZT, = 1.825 0.46BZT, = 1.757 -16 0.44BZT, = 1.633 -18 -20 ln Ccw , Số liệu thực nghiệm -6 ln(1/r - 1/rm) Tm 0.42BZT, = 1.598 ln(T - Tm) Hỡnh 3.8 l hm ca ln(T Tm) ca h xBZT T hỡnh 3.8, x tng, nhũe bin thiờn t 1.598 n 1.825, ngha l cú s chuyn pha nhũe vt liu, v gm th hin mc bt trt t cao Hỡnh 3.11 biu din phộp o (T) v tan ca mu 0.48BZT ti cỏc tn s 0.1, 1, 10, 100, 200, 500 kHz Khi tng tn s kớch thớch (theo chiu ca mi tờn ), vt liu th hin s tỏn sc in mụi tan 15000 0.48BZT 12000 0.15 9000 6000 0.20 f tăng 0.10 0.05 3000 0.00 20 40 60 80 100 120 T (C) Hỡnh 3.11 S ph thuc nhit ca hng s in mụi v tn hao in mụi ti cỏc tn s ca mu 0.48BZT S ph thuc vo tn s trng ngoi ca nhit Tm c mụ t bng nh lut Vogel - Fulcher (3.5) 13 Clean surfaces were observed for 0.48BZT-y samples with y = 0.00-0.15, and the grain size raised and reached maximum value of 21.6 àm at y = 0.15 Liquid phase was, however, appeared on the grain surface and boundary as y = 0.20, 0.25 It may be excess amount of ZnO nanoparticles during sintering accumulating at the surface and grain boundary to restrict particle size evolution Therefore, the experimental results indicate that solubility limit of ZnO nanoparticles in 0.48BZT ceramics is below 0.15 wt.% at sintered temperature of 1350oC 4.3.3 Dielectric properties (T) response shown in demonstrates broadenly ferro-paraelectric transition peaks 9000 12000 y = 0.00 y = 0.05 9000 6000 40 C 6000 y = 0.10 15000 o 3000 12000 3000 9000 9000 6000 6000 3000 12000 y = 0.15 12000 3000 12000 y = 0.20 y = 0.25 9000 9000 6000 6000 3000 3000 30 40 50 60 70 80 90 100 110 120 30 40 50 60 70 80 90 100 110 120 o T (oC) T ( C) Fig 4.8 (T) response of 0.48BZT-y system For y = 0.00 compound, a phase transition was observed around 40oC that is in the morphotropic phase boundary region of BZT-BCT system and seem to be related to to a tetragonal-rhombohedral phase transition It is supposed a part of material has changed into rhombohedral phase with small amount so that this phase was not identified in X-ray patterns but can be observed in (T) curve The mentioned phase transition was disappeared as raising content of ZnO nanoparticles It may be shifted to lower temperature As shown in fig 4.10, degree of diffuseness of the system was raised as y increasing and reached the maximum value of 1.796 at y = 0.15, then reduced 14 Số liệu thực nghiệm Đ-ờng làm khớp -8 y = 0.00, = 1.470 y = 0.05, = 1.542 -10 ln(1/r - 1/rm) -12 -14 -8 y = 0.01, = 1.559 y = 0.15, = 1.796 -10 -12 -14 -8 y = 0.20, = 1.454 y = 0.25, = 1.376 -10 -12 -14 4 ln(T - Tm) Fig 4.10 ln(1/ r 1/ r m ) as (LO3) A (LO3)/E A (TO3) E (TO2) C-ờng độ (a.u) A (TO1) A (TO2) a function of ln(T Tm ) at kHz for 0.48BZT-y system Fig 4.11 shows Raman spectrum of 0.48BZT-y system at room temperature y = 0.25 y = 0.20 y = 0.15 y = 0.10 y = 0.05 y = 0.00 200 400 600 800 1000 1200 Số sóng (cm-1) Fig 4.11 Raman spectrum of 0.48BZT-y system The Raman shift, , and half-width, FWHM, of the vibrational modes were specified by fitting Raman data with Lorentzian function A1(TO2) mode was considered as most sensitive to to the lattice distortion, while E(TO2) mode has been associated with the tetragonalcubic phase transition temperature FWHM[A1(TO2)] reflected broadened level of fer-paraelectric transition which was similar to degree of diffuseness (fig 4.13a) E(TO2) was shifted to lower wave number (Fig 4.13b) It means that substitution for B-site by Zn2+ results in reducing average B-O bonding energies Thus, tetragonal-cubic phase transition temperature was diminished 15 380 110 2.2 105 2.0 100 1.8 95 1.6 90 1.4 70 69 68 360 350 340 0.00 0.05 0.10 0.15 0.20 0.25 y (%) (b) 71 370 Tm (C) (a) 2.4 ETO2(cm) FWHM[A1(TO2)] FWHM[A1(TO2)] 115 67 ETO2(cm) 66 Tm (C) 65 0.00 0.05 0.10 0.15 0.20 0.25 y (%) Fig 4.13 ZnO nanoparticles concentration dependence of (a) FWHM[A1(TO2)], and , (b) [E(TO2)] and Tm 4.3.3 Ferroelectric characteristics Values of coercive field and remnant polarization are listed in table 4.8 Fig 4.8 Values of EC and Pr for 0.48BZT-y system y (%) 0.00 0.05 0.10 0.15 0.20 0.25 EC (kV/cm) 1.36 1.52 1.58 1.72 2.21 2.72 Pr (àC/cm ) 4.56 4.77 5.35 6.19 6.11 5.60 As we can see that, with creasing y, EC was continuously increased, whereas Pr was raised and obtained maximum value at y = 0.15, then reduced Generated oxygen vacancies due to substituting Zn2+ for B-site ions would be pinned the movement of ferroelectric domain walls As a result, value of coercive field was increased 4.3.4 Piezoelectric properties kp k31 kt k33 Qm 0.5 150 0.4 135 0.3 120 0.2 dij (pC/N) 400 165 |d31| d33 |g31| g33 12 350 10 300 250 200 150 0.00 0.05 0.10 0.15 0.20 0.25 0.00 0.05 0.10 0.15 0.20 0.25 y (%) gij (10-3Vm/N) k 0.6 Qm 0.7 y (%) Fig 4.18 k, Qm, dij, gij as a function of ZnO nano concentration, y 16 As mentioned above, the comprehensive analysis of X-ray diffraction, SEM images and dielectric properties have proved the ZnO addition induced lattice distortion and the degree of this local lattice distortion increased up to the maximal value as ZnO concentration raised up to 0.15 wt% It is supposed the spontaneous polarization in each nano-domain has contributed to overall spontaneous polarization that enhanced piezoelectric qualities of the material samples Beyond value of 0.15, the piezoelectric parameters are decreased due to residual amount of ZnO nanoparticles agglomerating at surface and grain boundary restricting grain size growth According to Ying-Chieh Lee et al., Zn2+ is substituted into the B-site to generate a doubly oxygen vacancy for neutralization The presence of charged oxygen vacancies would be pinned the movement of ferroelectric domain walls, and consequently to enhance Qm value 4.3 Effect of sintering temperature on structure, microstructure, and piezoelectric properties of 0.48BZT-0.15 composition 4.3.1 Surveying structure of 0.48BZT-0.15 ceramic as afuntion of sintering temperature Fig 4.19 illustrates XRD patterns of 0.48BZT-0.15 material sintered at various temperature (b) (002)T (200)R (200)T Mặt thoi 1450C 1400C 1450C 1400C 1350C 1350C Tứ giác C-ờng độ (đvtđ) (a) 1300C 1300C 20 30 40 50 60 70 80 44.7 45.0 45.3 45.6 45.9 Fig 4.19 (a) XRD pattern of 0.48BZT-0.15 ceramic sintered at different temperature in the range of (a) 20o-70o, (b) 44o-46o 17 All the samples have demonstrated pure perovskite phases The ceramics sintered at lower 1450oC possesses tetragonal phase For the samples sintered at 1450oC, there is coexistence of a tetragonal and rhombohedral phases with content of tetragonal phase of 67.3% Fig 4.21 shows the comparision sintering temperature dependence of grain size and density between 0.48BZT-0.15 and 0.48BZT ceramics According to that, grain size and density of 0.48BZT-0.15 material are lager than ones of 0.48BZT ceramic for every sintering temperature It is said that sintering behavior can be improved with a part of nano ZnO 4.3.2 Influence of sintering temperature on some piezoelectric properties of 0.48BZT-0.15 ceramics Table 4.12 Values of kp, k33, d33 of 0.48BZT-0.15 ceramic at different sintering temperature T (oC) kp k33 d33 (pC/N) 1300 0.32 0.48 340 1350 0.48 0.57 420 1400 0.49 0.61 474 1450 0.55 0.71 576 In general, the piezoelectric parameters of 0.48BZT-0.15 material increases simultaneously as rasing sintering temperature It could be consequence of improving microstructure when sintering temperature 18 varies Moreover, these parameters of 0.48BZT-0.15 composition are greater than ones of 0.48BZT sample at each sintering temperature (fig 4.23) Especially, values of kp and d33 for 0.48BZT-0.15 ceramic sintered at 1450oC are higher than that of Ba0.85Ca0.15Ti0.90Zr0.1O3 doped with micro-size ZnO sintered at 1480oC (d33 = 521 pC/N, kp ~ 0.48) which are reported by Wu el al Chapter Studying piezoelectric resonance characterization using Finite Element Method 5.1 Finite Element Method Studying physical systems results in frequently special differential equetions These equations can not be clearly solved, or their solutions could not be exact due to complicated boundary and domain conditions In orther to deal with this matters, numberial methods, exspecially Finite Element Method (FEM), could be effectly employed 5.2 Analyzing oscilation behaviour of disk-shape piezoelectric tranducers using FEM combinated with Comsol Multiphysics programs 5.2.1 Establishing a simulation problem for piezoelectric transducers 19 A simulation problem for piezoelectric transducers includes steps as follow Firstly, establish working regime for simulation program, then difine related variable and parameters Seconly, build a model and select materials for piezoelectric tranducer Selection of material was perform by inputing featured parameters into matries form After that, applying load on tranducer, setting up suitable boundary conditions, and choosing analysis types were perform Thirdly, find the solution for considered problems Finally, discus obtained results 5.2.3 Some results of using FEM and CM program to analyze oscillation behaviour for disk-shape tranducer The chosen material was 0.48BZT composition with density of = 5624 kg/m3 and other parameters listed in 5.1, 5.2 T(S) Table 5.1 Vaues of ij / o , dij, eij for 0.48BZT sample Tij (S) / o d31 5778 5198 eij (C/m2) dij (pC/N) 3306 3258 -188 d33 d15 e31 542 335 -7.6 e15 e33 13.1 26.4 Table 5.2 Elastic compliance and elastic stiffness constants of 0.48BZT ceramics sijE (10 12 cijE (1010 N/m2 ) m2 /N) E s11 E s12 E s13 E s 33 E s 44 E s 66 12.19 -4.27 -7.20 13.36 26.6 28.1 16.98 8.2 9.5 12.3 3.76 3.56 E E E E E E c13 c11 c12 c 33 c66 c 44 5.2.3.1 Evaluating oscillation region of 0.48BZT ceramic Fig 5.3 illustrates resonance spectra for 0.48BZT ceramics that got from experiment and FEM 20 10 FEM Thực nghiệm Z () 10 10 10 10 10 220 240 260 280 300 f (kHz) Fig 5.3 Resonance spectra for 0.48BZT ceramics resulted from experiment and FEM Table 5.3 lists values of resonance, fm, antiresonance, fn, frequencies, corresponding impedance values of Zm, Zn resulted form fig 5.3, and coupling facror kp Table 5.3 Coupling factor and resonance characterization Parameters fm fn kp Zm Zn Zn/Zm (unit) (kHz) (kHz) () () FEM 244.8 279.2 0.54 1.25 71978 57582 Experiment 250.2 282.4 0.52 7.62 8265 1085 There was a good suitability in results between experiment and simulation The difference between featured frequencies does not exceeded 2.2%, while the error of these coupling factors is 4.4% However, there are significantly differences in amplitudes of oscillation spectrums corresponding to two methods Zn/Zm fraction in simulation is 53 times as big as in experiment case Fig 5.4 Oscillation behavior of 0.48BZT disk at resonance frequency 21 Hỡnh 5.4 l nh 3D mụ t s dch chuyn ca bin t ỏp in ti tn s cng hng V c bn, bin t thc hin dao ng theo phng bỏn kớnh, song s dch chuyn trờn b mt bin t khụng u lm rừ iu ny, chỳng tụi kho sỏt trng thỏi cng hng ti biờn v chớnh gia ca bin t Hi ỏp ỏp in ca cỏc im ny v ca c bin t c nh lng bng 5.4 Bng 5.4 Cỏc giỏ tr c trng cng hng v h s lờn kt in - c ti cỏc v trớ trờn bin t v ca ton bin t fs fp kp Zm Zn Zn/Zm V trớ (kHz) (kHz) () () Biờn 244.8 257.2 0.35 3.77 46220 12259 Tõm 244.8 321.2 0.74 1.23 341510 277650 Ton phn 244.8 279.2 0.54 1.25 71978 57582 5.2.3.2 nh hng ca s bin i kớch thc bin t lờn tớnh cht cng hng ca h 0.48BZT Hỡnh 5.7 l ph cng hng ca mu 0.48BZT ng kớnh d = 10.8 mm, chiu dy t thay i khong (0.2-1.2) mm 10 (a) 0.2 mm 0.4 mm 0.8 mm 0.8 mm 1.0 mm 1.2 mm (b) Z () 10 10 10 -1 10 200 300 400 500 600 f (kHz) 700 800 600 650 700 f (kHz) 750 800 Hỡnh 5.7 Ph cng hng thu c t FEM ca a ỏp in vi cỏc chiu dy khỏc T hỡnh 5.7a, chiu dy tng, cỏc tn s cng hng v phn cng hng ca dao ng c bn gn nh khụng thay i, ngha l h s kp khụng b nh hng bi s thay i chiu dy mu Tuy nhiờn, 22 t = 0.4 mm 1.4 0.5 0.0 10.0 7.5 5.0 2.5 0.0 2.0 1.5 1.0 0.5 0.0 4.2 2.8 1.0 t = 0.6 mm 0.0 t = 0.8 mm 40 30 20 10 m) t = 0.2 mm 1.5 t = 1.0 mm t = 1.2 mm 2.0 1.5 1.0 0.5 0.0 300 400 500 600 700 800 300 400 500 600 700 800 f (kHz) m) m) m) m) 2.0 m) s dch chuyn tn s xy cỏc dao ng hi (hỡnh 5.7b), m c th l, cỏc tn s ny dch v phớa thp tng b dy ca mu Hỡnh 5.9 mụ t s ph thuc ca dch chuyn ton phn, , theo tn s, f, i vi a ỏp in 0.48BZT chiu dy thay i f (kHz) Hỡnh 5.9 dch chuyn ton phn, , l hm ca tn s, f i vi a ỏp in 0.48BZT theo cỏc chiu dy khỏc Cú th thy, cỏc bin t b dch chuyn mnh nht ti tn s cng hng Khi chiu dy, v ú, t s gia ng kớnh v chiu dy, d/t, thay i, dch chuyn ton phn ti tn s cng hng, r, thay i t 1.85 àm n 35.58 àm (bng 5.5) Bng 5.5 Giỏ tr r ng vi cỏc t s d/t d/t 54 27 18 13.5 10.8 r (àm) 1.98 4.78 9.88 35.58 2.08 1.85 5.3 Investigating the resonance properties of a cymbal transducer using 0.48BZT piezoelectric material 5.3.1 Introduction to Cymbal transducer The Cymbal transducer, a schematic of which is shown in fig 5.10, consist of a piezoceramic disk sandwiched between two metal en-caps The part of space between them is filled with air The low-displacement radial motion of piezoceramic disk caused a highdisplacement axial motion of metal end caps 23 Fig 5.10 describes the cross-section of a cymbal transducer in which do, ho are the diameter and thickness of air-filled space, and to is the thickness of the metal caps 5.3.2 Comparison of the oscillation behavior of disk-shaped and Cymbal tranducers Fig 5.11 shows the plots of total displacements versus frequency for the disk-shaped and Cymbal transducers The value of the resonance frequency is 93.1 kHz for the diskshaped tranducer, while that of Cymbal tranducer is 14.7 kHz The resonance properties of Cymbal transducer were also affected by the variation in their dimentions 5.4 Expiriment of preparing Cymbal transducer using 0.48BZT material Piezoelement 0.48BZT with d = 26.6 mm, t = 0.7 mm was fabricated using conventional technique End caps were made of copper with to = 0.2 mm, = 19.6 mm, and ho = 0.5 mm 24 Piezoelectric element and caps were contact with each other by a very thin layer of epoxy resin The plots of impedance versus frequency for Cymbal and disk transducers are given in fig 5.16 CONCLUSIONS We have developed manufacturing procedure and successfully fabricated the non lead piezoelectric ceramics xBaZr0.2Ti0.8O3-(1x)Ba0.7Ca0.3TiO3 (abbreviated as xBZT) sintered at 1450oC Some important results are listed as below + As increasing BZT content, the crystal symmetry change from a tetragonal phase to rhombohedral one Moreover, there is a coexistence of tetragonal and rhombohedral phases at x = 0.48 It is permissible to predict that MPB is located at 0.48BZT composition This result I different from previous work, where MPB composition is x = 0.50 This is the first new contribution of our thesis + A full set of eleastic, dielectric, piezoelectric parameters were calculated For 0.48BZT sample, the high values of d33, d31, d15, k33, kp, kt, k15, k31 are 542 pC/N, -188 pC/N, 335 pC/N, 0.66, 0.52, 0.55, 0.45, 0.30, respectively These results confirm that xBZT materials are excellent candidates to replace for Pb-based materials This is the second new point of our thesis 25 + ZnO nanoparticles doped 0.48BZT ceramics were successfully using conventional technique As a result, 0.48BZT doped with 0.15 wt% ZnO nanoparticles sample sintered at temperature of 1350oC possesses very high piezoelectric parameters The values of d33, k33, kp for this composition are 420 pC/N, 0.57, 0.48, respectively For sample sintered at 1450oC, excellent values of d33, kp are 576 pC/N, 0.55, respectively This is the third new information of our thesis + The combination of finite element method and COMSOL Multiphysics was employed to study oscillation behaviour of diskshaped and Cymbal transducer based 0.48BZT ceramic The simulation results are well appropriate with the results from experiments that assert remarkable piezoelectric properties of the 0.48BZT material The material system is suitable for hydro-acoustic applications + The experiences in preparing Cymbal transduce used 0.48BZT piezoelectric element were implemented, and the shift in resonance frequency of Cymbal transducer are examined Consequently, Cymbal transducer could be work at lower frequency of about 6.6 times compared to that of the same diameter disk-shaped transducer This is the fourth new contribution of our thesis Based on obtained results, we suggest two following matters Firstly, continuing to study how to lower the sintering temperature of the materials to save costs and increase the competitiveness in applications Secondly, improving the Curie temperature to expand application range for the materials The proper settlements of two major drawbacks make BZT-BCT systems become the excellent materials for application 26 PUBLICATIONS Articles in ISI list Dang Anh Tuan, Nguyen Trong Tinh, Vo Thanh Tung and Truong Van Chuong, Ferroelectric and Piezoelectric Properties of Lead-Free BCT- xBZT Solid Solutions, Materials Transactions, Vol 56, No (2015) pp 1370-1373 Dang Anh Tuan, Vo Thanh Tung, Truong Van Chuong, Nguyen Trong Tinh, Nguyen Thi Mai Huong, Structure, Microstructure and Dielectric Properties of Lead-free BCTxBZT Ceramics near the Morphotropic Phase Boundary, Indian Journal of Pure & Applied Physics, Vol 53, June 2015, pp 409-415 Dang Anh Tuan, Vo Thanh Tung, Truong Van Chuong, Le Van Hong, Properties of Lead-free BZT-BCT ceramics synthesized using nanostructured ZnO as a sintering aid, International Journal of Modern Physics B (2015) (Acepted) Other articles Dang Anh Tuan, Vo Thanh Tung, Le Van Phuong, Analyzing 2D Structure Images of Piezoelectric Ceramics Using ImageJ, International Journal of Materials and Chemistry 2014, 4(4): 88-91 Vo Thanh Tung, Nguyen Trong Tinh, Nguyen Hoang Yen, Dang Anh Tuan, Evaluation of Electromechanical Coupling Factor for Piezoelectric Materials Using Finite Element Modeling, International Journal of Materials and Chemistry 2013, 3(3): 59-63 Vo Thanh Tung, Nguyen Trong Tinh, Nguyen Hoang Yen, Le Thi Ngoc Bao and Dang Anh Tuan, Finite Element Modeling in Analyzing Physical Properties of the Pb-Free Piezoelectric 27 Materials, Journal of Materials Science and Engineering A (4) (2013) 283-289 Vo Thanh Tung, Nguyen Trong Tinh, Truong Van Chuong, Nguyen Thi Mai Hng, Dang Anh Tuan, Le Van Truyen, Investigation the Dimensional Ratio Effect on the Resonant Properties of Piezoelectric Ceramic Disk, Journal of Modern Physics, 2013, 4, 1627-1631, Vo Thanh Tung, Dang Anh Tuan, Nguyen Hoang Yen, Le Thi Ngoc Bao, Finite Element Method in Analyzing the Vibration Modes of Piezoelectric Ceramics, Hue University Journal of Science, Vol 84, No (2013) Dang Anh Tuan, Vo Thanh Tung, Le Thi Thu Hien, Le Xuan Diem Ngoc, Hoang Quoc Khanh, Truong Van Chuong, An Acoustic Cymbal Transducers Based On Lead-Free Piezoelectric Materials BZT-xBCT, SPMS2015, Ho Chi Minh City [...]... thnh cụng vt liu ỏp in xBZT- (1- x)BCT hay xBZT thiờu kt 1450oC v nghiờn cu nh hng ca t phn BZT n cỏc tớnh cht vt lý ca h ny 25 Khi tng t phn, x, ca BZT trong dung dch rn, cu trỳc ca vt liu thay i t t giỏc sang mt thoi Thnh phn ng vi x = 0.48 tn ti ng thi pha mt thoi v pha t giỏc, v chỳng tụi d oỏn õy l thnh phn biờn pha hỡnh thỏi hc, khỏc vi mt cụng b trc ú khi cho rng, biờn pha hỡnh thỏi hc ca h nm... mentioned fact, the chosen title of the thesis is synthesis and study the physical properties of modified xBZT- (1- x)BCT systems The objects selected in this thesis are the lead-free xBZT- ( 1x)BCT piezoelectric materials Desertations contetns include Firstly, research on preparation of modified xBZT- (1- x)BCT Secondly, investigating ferroelectric dielectric, piezoelectric properties of the materials Thirdly,... 0.30 140 0.20 dij (pC/N) 600 d33 |d31| d15 g33 |g31| g15 500 10.0 400 8.0 300 6.0 200 100 12.0 gij (10 -3 Vm/N) 0.80 0.40 0.44 0.48 0.52 0.56 x 0.40 0.44 0.48 0.52 0.56 x 4.0 Hỡnh 3.18 S ph thuc nng BZT ca cỏc thụng s ỏp in 11 (10 1) 30 50 60 (11 2) (201) (200) (11 0) (10 2) 40 (10 3) Lục giác (002) C-ờng độ (10 0) Cú th thy, cỏc thụng s ỏp in, c u thay i theo t phn BZT v t cc tr ti thnh phn 0.48BZT Tớnh cht... T (oC) T (oC) Hỡnh 4.8 S ph thuc (T) h 0.48BZT-y i vi mu y = 0.00, cú mt im chuyn pha khỏc gn 40oC nm trong vựng MPB ca BZT-BCT Chuyn pha ny liờn quan n chuyn pha t giỏc - mt thoi Cú th, mt lng vt liu rt nh chuyn sang pha mt thoi nờn phộp o nhiu x tia X khụng ghi nhn c m ch th hin trờn ng cong (T) Khi y tng, im chuyn pha ny bin mt, cú th nú dch chuyn v phớa nhit thp nhũe ca vt liu c th hin trờn hỡnh... using a resonance method and calculated following formulae in the IEEE standard 2.2 Procedure for preparing xBZT- (1- x)BCT ceramics The chosen raw materials with high purity (>99%, Mecrk) are BaCO3, CaCO3, TiO2, ZrO2 They were weighted for an equimolar in stoichiometric proportion of xBaZr0.2Ti0.8O3 -(1- x)Ba0.7Ca0.3TiO3, where x is a molar percent of BZT The mixture was milled in a planetary milling machine... hin trờn hỡnh 4.10 Theo ú, khi y tng, tng, t giỏ tr cc i ti thnh phn y = 0.15, sau ú gim Số liệu thực nghiệm Đ-ờng làm khớp -8 y = 0.00, = 1.470 y = 0.05, = 1.542 -10 ln(1/r - 1/rm) -12 -14 -8 y = 0.01, = 1.559 y = 0.15, = 1.796 -10 -12 -14 -8 y = 0.20, = 1.454 y = 0.25, = 1.376 -10 -12 -14 Hỡnh 4.10 ln(1/ r 1 1/ 2 3 r m ) l 4 1 ln(T - Tm) 2 3 4 hm ca ln(T Tm ) ti 1 kHz ca h vt liu 0.48BZT-y 14... khi mode E(TO2) c cho l cú mi liờn h vi nhit chuyn pha t giỏc - lp phng FWHM[A1(TO2)] phn ỏnh mc tri rng ca nh chuyn pha st in-thun in tng t nh nhũe (hỡnh 4.13a) Mt khỏc, mode E(TO2) dch v phớa s súng thp khi nng ZnO nano tng Ngha l, s thay th cỏc ion v trớ B bi ion Zn2+ ó lm gim nng lng liờn kt trung bỡnh B-O trong mng ABO3 Vỡ vy, nhit chuyn pha t giỏc-lp phng gim (hỡnh 4.13b) 380 (a) 2.4 110... 45.0 45.3 45.6 45.9 2 Hỡnh 4.19 (a) XRD ca vt liu 0.48BZT-0.15 trong khong (a) 20o-70o, (b) 44o-46o Nhỡn chung, vt liu s hu pha perovskite thun tỳy Cỏc mu c nung nhit di 1450oC cú i xng t giỏc Riờng i vi mu thiờu kt 1450oC cú s tn ti ng thi ca pha t giỏc v mt thoi vi nng pha t giỏc l 67.3% Hỡnh 4.21 so sỏnh s thay i c ht v t trng theo nhit thiờu kt ca vt liu 0.48BZT-0.15 v 0.48BZT Cỏc i lng ny... vi phng trỡnh (3.5) ln(f (Hz)) 14 x = 0.48 12 10 8 Số liệu thực nghiệm Đ-ờng làm khớp 6 4 88 90 92 94 96 98 100 Tm (oC) Hỡnh 3.12 lnf l hm ca Tm lm khp vi nh lut Vogel Fulcher i vi thnh phn 0.48BZT S phự hp khỏ tt gia s liu thc nghim vi h thc Vogel Fulcher cho thy, rng h thc ny cú th c s dng gii thớch trng thỏi chuyn pha nhũe trong h vt liu xBZT tng t nh trng thỏi ca cỏc thy tinh lng cc cú s dao... thy, trng thỏi thiờu kt v mt s tớnh cht vt lý ca thnh phn ny c ci thin v tt hn i vi thnh phn 0.48BZT khi nhit thiờu kt tng c bit, mu 0.48BZT-0.15 c thiờu kt 1450oC cú h s d33 v kp ln lt l 576 pC/N v 0.55, cao hn hn cỏc tham s cựng loi ca vt liu Ba0.85Ca0.15Ti0.90Zr0.1O3 pha tp ZnO kớch thc micro thiờu kt 1480oC (d33 = 521 pC/N, kp ~ 0.48) 26 Ln u tiờn, lý thuyt phn t hu hn kt hp vi chng trỡnh mụ