- Email: [email protected]
Properties of La2O3-Doped PNSZT Piezoelectric Ceramics Having Tetragonal and Rhombohedral Coexistent Phases
JOURNAL OF RARE EARTHS V o l . 2 4 , Spec. Issue, Dec. 2006, p . 2 5 5
Properties of La2O3-Doped PNSZT Piezoelectric Ceramics Having Tetragonal and Rhombohedra1 Coexistent Phases Huang Xinyou (R-$fiFikr) * , Gao Chunhua (&&*), Chen Zhigang (Plf,&alq) (School of Materials Science and Engineering,Jiangsu University, Zhenjiang 212013, China)
Abstract : The relationship between composition and the electric mechanical properties for LazO3-doped lead niobium stibium zirconate titanate( LaaO3-doped PNSZT) piezoelectric ceramics, in which there are tetragonal and rhombohedral coexistent phases, was studied. A series of piezoelectric ceramics with good properties was obtained, having dielectric constants(€ = 1500 2500), plane electromechanical coupling factor( K , = 0.45 0 . 6 5 ) , mechanical quality factor( Qn, = 500 1600). These materials are used for making ultrasonic sensor and filter, and marine acoustic launching and receiving device, and so on. It has been explored that the influence of composition on the lattice constant and phase composition of LazO3-doped PNSZT piezoelectric ceramics by XRD(X-ray diffraction) . The character of dielectric constant changing of La~O3-dopedPNSZT piezoelectric ceramics before polarization and after polarization was studied . The affecting mechanism about composition on the electric machine properties of phase coexistent La203-doped PNSZT piezoelectric ceramics was analyzed and discussed.
-
-
-
Key words : ceramics ; La203 ; lead niobium stibium zirconate titanate ; piezoelectric ceramics : rare earths Article ID: 1002 - 0721(2006) - 0255 - 04 CLC number: TQ174 Document code : A
There are good electric mechanical properties in the lead niobium stibium zirconate (PNSZT) p'iezoelectric It is able to be widely used for making automobile order reading device, filter element, marine acoustic launching and receiving device, and so on. In order to fabricate the piezoelectric ceramics for various use, adjusting composition is a suitable method. The nearby of x = 0.53 is tetragonal and rhombohedral phase boundary of Pb (Zr,Til- ) 0, (PZT) . The structure of tetragonal and rhombohedral is the close. They are obtained from cubic perovskite structure by small distortion, and this phase boundary is called morphotropic phase boundary ( MPB)[2'. The component near phase boundary has tetragonal and rhombohedral coexistent, there are more orientations in the component, the arranging extent of electric dipole moment along electric field is higher, and there is high piezoelectric properties near morphotropic phase boundary, after polarization'" 41 . It is also MPB in ternary system and quaternary system piezoelectric It is important to study MPB piezoelectric ceramics, s o , many researchers studied MPB piezoelectric c e r a m i c ~ [ ~,- there ~I is little study about the influence of composition (Zr/Ti and ( Sbo.sNb0.5 ) ) on the structure and properties of La203-doped PNSZT
-
*
Received date: 2006 - 06 06;revised date: 2006 - 09 - 19 Biography: Huang Xinyou (1963 ) , Male, Master, Professor Corresponding author (E-mail: [email protected])
-
piezoelectric ceramics having tetragonal and rhombohedral coexistent phases (MPB ) . To obtain great piezoelectric properties, usually selecting Zr/Ti near morphotropic phase boundary ( MPB ) ( tetragonal and rhombohedral coexistent phase). The MPB is an area due to fabricating technology[21. In order to find the character and mechanism of the composition influencing the properties and structure of PNSZT piezoelectric ceramics near MPB . In this paper, the influence of Zr/Ti and ( Sbo.5Nbo,5) on the properties and structure of La203-doped PNSZT piezoelectric ceramics near MPB was studied, and its influencing mechanism was explored, by selecting La203-doped PNSZT piezoelectric ceramics near MPB ceramics. It provided the basis for the preparation of new kinds of piezoelectric ceramics.
1 Experimental The experimental fornula was PNSZT piezoelectric ceramics doped with certain La203,SrC03, Mn02 and excess w (Pb04)is 1.O% , adjusting ZrlTi (mole ratio) and ( S4,5Nb., ) (mole ) . The starting materials were chemical materials. The sample were prepared by means of conventional containing lead piezoelectric ceramic technology. The sample for the measurment of piezoelec-
.
256
JOURNAL OF RARE EARTHS, Vol. 2 4 , Spec. Issue, Dec 2006
-
tric properties was poled in silicon oil at 110 130 "c under 3 - 4 kV-mm for 15 20 min. The piezoelectric ceramics studied is suitable for making ultrasonic sensor, middle wide hand filter element, marine acoustic launching and receiving device, and so on. After the sample poling and aging for 24 h , the plane electromechanical coupling factor ( K , ) , the dielectric constant ( E ) , the mechanical quality factor ( Q m )of sample were measured by transmission circuit method. The frequency temperature coefficient ( Tkfr ) of sample was measured by increasing temperature and maintaining temperature method. The lattice constant and phase composition of sample were determined by using an X-ray diffractometer (XRD) (Li Xue D/max-rB) . The sample used was removed silver electrode and ground to pass through 250 BSS mesh sieve. The diffracted data were used for determining the lattice constant and phase composition by computer.
'
-
60
-
50
-
40..
30
-
Fig.2 Zr/Ti vs
E ,
K,,
Qm
of PNSZT ((Sb112Nb112) =0.03)
{
?IM1
2 Results and Analysis The relationship between Zr/Ti and E , K , , Qmof La203-doped PNSZT piezoelectric ceramics which ( Sbo 5Nbo 5 ) are 0.02, 0.03, 0.04 rnol respectively is listed in Figs. 1 3 . The Zr/Ti of maximum piezoelectricity sample is 54/44 ( mol ) while ( Sbo Nb, ) is 0.02 mol, whose E is 2200, K , is 0.54 and Q m is 560. The Zr/Ti of maximum piezoelectricity sample is 55/42( mol) while (Sbo sNbo 5 ) is 0.03 mol, whose E is 1910, K , is 0.48 and Qmis 620. The Zr/Ti of maximum piezoelectricity sample is 54/40 ( mol ) while (Sbo Nbo 5 ) is 0.04 mol, whose E is 1720, K , is 0.45 and Qmis 750. It is obvious that Zr/Ti of maximum piezoelectricity sample increases, the value of maximum K , and E dccreases and Qmincreases, while ( Sbo 5Nbo 5 ) additive amount increasing. Fig. 4 shows the relationship between Zr/Ti and Tkfi of PNSZT with various ( Sbo Nbo ) amount . It
-
I
*
I
P,700
R
500
is obvious that the changing law of Tkji- vs. ZrlTi is similar while ( Sbo,5Nbo.5)amount is certain, the Tkfr is zero while Zr/Ti is a certain value, and obtaining high temperature stable piezoelectric ceramics. The dielectric constant changing before and after polarization is given in Table 1, when ( Sbo 5Nb0.5) is 0.02 mol. According to Table 1, only the E of the sample ( Zr/Ti = 56/42) decreases after polarization. The E of the other samples (other Zr/Ti) increases, only increasing range is different while Zr/Ti is different after polarization. The dielectric constant increasing range of the sample is maximum while Zr/Ti = 52/ 46 and is minimum while Zr/Ti = 54/44, after polarization. The sample (after polarization) with various Zr/Ti was analyzed by XRD(X-ray diffraction) while (Sbo.5 Nb0.5) is 0.02 mol . According to analyzing result, the Table 1
a!
Change of dielectric constant in various ZdTi samples before and after polarization *
ZrITi
52/46
53/45
54144
56/42
€1
1465
1842
2081
1550
€2
1580
1969
2209
1485
(€2 -E,):EI/%
+7.8
+6.9
+6.2
-4.2
*
is dielectric constant before polarization, after polarization EI
€2
is dielectric constant
H w n g X Y et a1 . Properties of La20rDoped PNSZT Piezoelectric Ceramics
sample is composed of tetragonal and rhombohedral phases coexistent. It is obvious that the phase boundary is a certain range, and their quantitative characteristic line intensity of XRD patterns ( I T , I R ) is listed in Table 2. The phase content for tetragonal and rhombohedral phases was calculated by formula fT = I T / ( Z R + IT)and f R = 1 - f T , and is listed in Table 2 . According to Table 2. the tetragonal phase content continuously decreases, and the rhombohedral phase content increases, and while ZrITi increasing. Tetragonal phase content is approximately equal to rhombohedral phase content while Zr/Ti is 54/44. The sample (after polarization) with various Zr/Ti was analyzed by XRD while (Sbo.sNbo.s)is 0.02 mol. The result analyzed was dealt with computer according to Powder X soft ware, and the lattice constants of sample with various Zr/Ti were obtained and listed in Table 3. The lattice constants of sample with various Zr / Ti were determined by means of indexing method . 0 (Sb,,2Nb,,)=0.02
* (Sb,,q,3=0.03
a (Sb,,*q,*)=0.04
-40 -60
d
Various (Sb,,Nb,,)
Fig.4
amount, ZdTi v s . and TMr of
PNSZT
Table 2 Phase composition of various ZdTi sample" 52/46 53/45 54/44 56/42
651 639 628 610
466 543 62 1 672
58.30 54.04 50.27 47.60
41.90 45.96 49.73 52.40
* I T , In are separately quantitative characteristic line XRD intensity, f~, fR are separately phase content for tetragonal phase and rhombohedral phase
Table 3 Lattice constant of various Zr/Ti sample ' ~~
~~
&/Ti
56/42
54/44
53/45
52/46
a T
4.0482 4.1030 4.0727 1.0135 89.703
4.0381 4.1180 4.0696 1.0200 89.682
4.0320 4.1210 4.0604 1.0221 89.673
4.0270 4.1240 4.0550 1.0241 89.669
CT UR
CT/UT
do) *
UT,
CT are tetragonal phase lattice constant,
dral phase lattice constant
UR, a
are rhombohe-
257
In order to decrease inaccuracy, the lattice constant was calculated by XRD patterns data which Bragg angle is close to high angle of 90°[91. According to Table 3 , the lattice constants ( a T , cT, aR, (Y ) of sample are decreased and the axial ratio ( c T / u T ) of sample is increased while Zr/Ti decreasing.
3 Discussion The ionic radius of Sb3' , Nb5+ are separatively rsb3+ = 0.076 nm , rNb5+= 0.069 nm . The ionic radius of ( Sbl/2Nb1/2) is 0.073 nm . The ionic radius of Zr4+ , Ti4+are rzp+ = 0.079 nm, rT++ = 0.086 nm separatively. So, (Sbl,,NbIl2) can enter into (Zr, Ti) site. Sb3+is acceptor ion and entering (Zr, T i ) , NbS+ is donor ion and entering (Zr , Ti ) , and they produce compensation effect, The ratio between electrovalent and ionic radius ( z / r k ) (55.2) of ( Sbl/2Nbl/2)4+ ( z is ionic valance, rk is ionic radius) is more than z/rk (48.8) of (Zr, Ti)4+(Zr/Ti = 56/42 52/46), the bond strength of ( Sb,,,Nbvz) - 0 is stronger than that of (Zr , Ti) - 0 , ( Sbl,2Nbl,2)4+moving temperature is higher than ( Zr, Ti ) moving temperature"]. So, (Sb112Nbl/2)replacing (Zr, Ti) can raise the Curie temperature, increase temperature stable and shift phase boundary to Zr-rich region"]. At the same time, the dielectric constant at room temperature is decreased. The z / r k of ( SblRNbl/,) ion is more than that of (Zr, Ti) ion. The different effect is not neglected when (Sbl,,Nbl,,) amount is high, and they enhance (Zr , T i ) - 0 bond, while coefficient of elasticity (SllE)and K , decreasing. It is difficult for domain to swich, so the dielectric loss decreases, and the mechanical quality factor ( Qm)increases. The experimental result shows that the electric mechanical properties of sample is changed regularly, while ( Sbl/,Nb1,) amount changing. The K , and E of sample are maximum, and Qm of sample is minimum when Zr/Ti is certain amount. The changing law for Tkfr vs Zr/Ti is similar, and the piezoelectric ceramics with minimum Tkfr value may be obtained. In tetragonal phase, spontaneous strain is A Z = c / a - 1 . In rhombohedral phase, spontaneous strain is A Z = id2 - a [ ' ] . In tetragonal phase area, c / a decreases, C Z decreases and then coercive electric field decreases. The motion of domain is easily, the 90 degree domain rotation rate of the sample increases, remainder polarization intensity ( P , ) increases and K , increases, while Zr/Ti in~reasing'~' lo' . The remainder polarization intensity ( P , ) of sample decreases and K , decreases, while c / a decreases greatly. In rhombohedral phase area, the P , an? K , of sample start increas-
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JOURNAL OF RARE EARTHS, Vol. 24, Spec. Issue, Dee. 2006
ing and then decreasing while Zr/Ti increasing. Because MPB is tetragonal phase and rhombohedral phase coexistent, the spontaneous polarization orientation increases and K , is maximum at MPB. The maximum value of dielectric constant in MPB is due to D = 0, of which D is the coefficient of dielectric constant thermodynamics unfolding formula"' . MPB is not a line, but is wide componental range, and the wide and narrow of componental range is related to technology factor. There are tetragonal phase and rhombohedral phase coexistent in the componental range. There are big tetragonal and rhombohedral phase coexistent range due to component variation in piezoelectric ceramics prepared by conventional milling mix method, and the componental range for Zr/Ti is 50/50 55/45. MPB is truly component, in which two kinds of phase are equal. The K , and E of the sample are maximum when two kinds of phases are equal, but the K , and E of the sample are small in other phase component ceramics. The changing character of dielectric constant before polarization and after polarization is determined by phase component for various Zr/Ti sample'31. The dielectric constant increases after polarization in tetragonal phase, the dielectric constant decreases after polarization in rhombohedral phase. The dielectric constant of the sample containing more tetragonal phase increases after polarization. In the reverse, the dielectric constant of the sample with more rhombohedral phase decreases after polarization.
-
4
3 . The componental range of tetragonal phase and rhombohedral phase coexist because component variety is big by conventional containing lead piezoelectric ceramic preparation technique. There are maximum piezoelectricity in the ceramics whose tetragonal phase is equal to rhombohedral phase. 4. The dielectric constant of the sample which has more tetragonal phases than rhombohedral phases increases after polarization. The dielectric constant of the sample which has more rhombohedral phases than tetragonal phases decreases after polarization.
References : [ 11 Tecuro Tanaka, et al . Piezoelectric Ceramic Materials
[2]
[3]
41
51
Conclusions
The influence of Zr/Ti and ( Sho.sNbo5 ) amount on the structure and properties of La203-dopedPNSZT ceramics having tetragonal phase and rhombohedral phase coexistent ( MPB ) were explored, the conclusions were obtained as follows: 1. The influence of Zr/Ti on the structure and properties of Laz03-doped PNSZT ceramics having tetragonal phase and rhombohedral phase coexistent are big . The lattice constants ( u T , u R , (Y ) of Laz03doped PNSZT ceramics decrease while Zr/Ti decreasing. The lattice constants ( cT, c J u T ) of La203-doped PNSZT ceramics increase while Zr/Ti decreasing. 2 . The influence of (Sb1,,Nbl,,) on the properties of La203-doped PNSZT ceramics is big, while ( Sbl,, Nbllz) additive amount increasing, the mechanical quality factor ( Qm) and temperature stability electric ceramics can be raised.
[6]
[ 71
[8]
[9]
[ 101
[ M I . Chen Junyan, Wang Yujun (Translation). Beijing: Science Press, 1982. 37. Zhang Peilin, Zhong Weilie, Wang Yuguo, et al. Piezoelectric Material and Device Physics [ M ] . Jinan: Shandong Science Technique Press ( in Chin. ) , 1997. 156. Lu Peiwen, Huang Xinyou. The influence of excess PbO and atmosphere powder on the properties and microstructure of lead zirconate titanate ceramics [ J]. Journal of Instrument Materials (Journal of Functional Materials at present), 1990, 2 1 ( 6 ) : 346. Huang Xinyou, Gao Chunhua. Study on polarization of lead niobium-stibium zirconate-titanate piezoelectric ceramics having tetragonal and rhombohedral phases coexistent [ J ] . Journal of the Chinese Ceramic Society ( i n Chin.), 2001, 2 9 ( 5 ) : 422. Lu Cuimin, Sun Qingchi, Xu Mingxia, et al. Properties of PMSZT piezoelectric ceramics near rnorphotropic phase boundary [J].Journal of Rare Earths, 2004, 22 (Spec.): 120. Li Zhenrong, Zhang Liangying, Yao Xi. Dielectric pyroelectric and piezoelectric properties in Pb ( NiliJ Nb,,, ) 03-PbTi03 system near morphotropic phase boundary [ J ] . Journal of the Chinese Ceramic Society (in Chin. ) , 2000, 2 8 ( 3 ) : 199. Gao Chunhua , Huang Xinyou . The influence of various dopant on the dielectric and piezoelectric properties in PSN-PSZT system near morphotropic phase boundary [J]. China Ceramic Industry (in Chin. ) , 2002, 9 ( 4 ) : 20. Xia Feng, Yao Xi. Phase structure and dielectric piezoelectric properties of PZN-BT-PZT ceramics [ J ]. Journal of the Chinese Ceramic Society ( in Chin. ) , 1999, 27(2): 172. Yang Nanru. Inorganic Non-metallic Material Test Method [ M] . Wuhan: Wuhan Industrial University Press (in Chin.), 1993. 76. Huang Xinyou, Lu Peiwen. XRD study on polarization of lead niobium-stibium zirconate-titanate ceramics [ J ] . Bull. Chin. Ceram. SOC., 1993, 12(4): 19.
Properties of La2O3-Doped PNSZT Piezoelectric Ceramics Having Tetragonal and Rhombohedra1 Coexistent Phases Huang Xinyou (R-$fiFikr) * , Gao Chunhua (&&*), Chen Zhigang (Plf,&alq) (School of Materials Science and Engineering,Jiangsu University, Zhenjiang 212013, China)
Abstract : The relationship between composition and the electric mechanical properties for LazO3-doped lead niobium stibium zirconate titanate( LaaO3-doped PNSZT) piezoelectric ceramics, in which there are tetragonal and rhombohedral coexistent phases, was studied. A series of piezoelectric ceramics with good properties was obtained, having dielectric constants(€ = 1500 2500), plane electromechanical coupling factor( K , = 0.45 0 . 6 5 ) , mechanical quality factor( Qn, = 500 1600). These materials are used for making ultrasonic sensor and filter, and marine acoustic launching and receiving device, and so on. It has been explored that the influence of composition on the lattice constant and phase composition of LazO3-doped PNSZT piezoelectric ceramics by XRD(X-ray diffraction) . The character of dielectric constant changing of La~O3-dopedPNSZT piezoelectric ceramics before polarization and after polarization was studied . The affecting mechanism about composition on the electric machine properties of phase coexistent La203-doped PNSZT piezoelectric ceramics was analyzed and discussed.
-
-
-
Key words : ceramics ; La203 ; lead niobium stibium zirconate titanate ; piezoelectric ceramics : rare earths Article ID: 1002 - 0721(2006) - 0255 - 04 CLC number: TQ174 Document code : A
There are good electric mechanical properties in the lead niobium stibium zirconate (PNSZT) p'iezoelectric It is able to be widely used for making automobile order reading device, filter element, marine acoustic launching and receiving device, and so on. In order to fabricate the piezoelectric ceramics for various use, adjusting composition is a suitable method. The nearby of x = 0.53 is tetragonal and rhombohedral phase boundary of Pb (Zr,Til- ) 0, (PZT) . The structure of tetragonal and rhombohedral is the close. They are obtained from cubic perovskite structure by small distortion, and this phase boundary is called morphotropic phase boundary ( MPB)[2'. The component near phase boundary has tetragonal and rhombohedral coexistent, there are more orientations in the component, the arranging extent of electric dipole moment along electric field is higher, and there is high piezoelectric properties near morphotropic phase boundary, after polarization'" 41 . It is also MPB in ternary system and quaternary system piezoelectric It is important to study MPB piezoelectric ceramics, s o , many researchers studied MPB piezoelectric c e r a m i c ~ [ ~,- there ~I is little study about the influence of composition (Zr/Ti and ( Sbo.sNb0.5 ) ) on the structure and properties of La203-doped PNSZT
-
*
Received date: 2006 - 06 06;revised date: 2006 - 09 - 19 Biography: Huang Xinyou (1963 ) , Male, Master, Professor Corresponding author (E-mail: [email protected])
-
piezoelectric ceramics having tetragonal and rhombohedral coexistent phases (MPB ) . To obtain great piezoelectric properties, usually selecting Zr/Ti near morphotropic phase boundary ( MPB ) ( tetragonal and rhombohedral coexistent phase). The MPB is an area due to fabricating technology[21. In order to find the character and mechanism of the composition influencing the properties and structure of PNSZT piezoelectric ceramics near MPB . In this paper, the influence of Zr/Ti and ( Sbo.5Nbo,5) on the properties and structure of La203-doped PNSZT piezoelectric ceramics near MPB was studied, and its influencing mechanism was explored, by selecting La203-doped PNSZT piezoelectric ceramics near MPB ceramics. It provided the basis for the preparation of new kinds of piezoelectric ceramics.
1 Experimental The experimental fornula was PNSZT piezoelectric ceramics doped with certain La203,SrC03, Mn02 and excess w (Pb04)is 1.O% , adjusting ZrlTi (mole ratio) and ( S4,5Nb., ) (mole ) . The starting materials were chemical materials. The sample were prepared by means of conventional containing lead piezoelectric ceramic technology. The sample for the measurment of piezoelec-
.
256
JOURNAL OF RARE EARTHS, Vol. 2 4 , Spec. Issue, Dec 2006
-
tric properties was poled in silicon oil at 110 130 "c under 3 - 4 kV-mm for 15 20 min. The piezoelectric ceramics studied is suitable for making ultrasonic sensor, middle wide hand filter element, marine acoustic launching and receiving device, and so on. After the sample poling and aging for 24 h , the plane electromechanical coupling factor ( K , ) , the dielectric constant ( E ) , the mechanical quality factor ( Q m )of sample were measured by transmission circuit method. The frequency temperature coefficient ( Tkfr ) of sample was measured by increasing temperature and maintaining temperature method. The lattice constant and phase composition of sample were determined by using an X-ray diffractometer (XRD) (Li Xue D/max-rB) . The sample used was removed silver electrode and ground to pass through 250 BSS mesh sieve. The diffracted data were used for determining the lattice constant and phase composition by computer.
'
-
60
-
50
-
40..
30
-
Fig.2 Zr/Ti vs
E ,
K,,
Qm
of PNSZT ((Sb112Nb112) =0.03)
{
?IM1
2 Results and Analysis The relationship between Zr/Ti and E , K , , Qmof La203-doped PNSZT piezoelectric ceramics which ( Sbo 5Nbo 5 ) are 0.02, 0.03, 0.04 rnol respectively is listed in Figs. 1 3 . The Zr/Ti of maximum piezoelectricity sample is 54/44 ( mol ) while ( Sbo Nb, ) is 0.02 mol, whose E is 2200, K , is 0.54 and Q m is 560. The Zr/Ti of maximum piezoelectricity sample is 55/42( mol) while (Sbo sNbo 5 ) is 0.03 mol, whose E is 1910, K , is 0.48 and Qmis 620. The Zr/Ti of maximum piezoelectricity sample is 54/40 ( mol ) while (Sbo Nbo 5 ) is 0.04 mol, whose E is 1720, K , is 0.45 and Qmis 750. It is obvious that Zr/Ti of maximum piezoelectricity sample increases, the value of maximum K , and E dccreases and Qmincreases, while ( Sbo 5Nbo 5 ) additive amount increasing. Fig. 4 shows the relationship between Zr/Ti and Tkfi of PNSZT with various ( Sbo Nbo ) amount . It
-
I
*
I
P,700
R
500
is obvious that the changing law of Tkji- vs. ZrlTi is similar while ( Sbo,5Nbo.5)amount is certain, the Tkfr is zero while Zr/Ti is a certain value, and obtaining high temperature stable piezoelectric ceramics. The dielectric constant changing before and after polarization is given in Table 1, when ( Sbo 5Nb0.5) is 0.02 mol. According to Table 1, only the E of the sample ( Zr/Ti = 56/42) decreases after polarization. The E of the other samples (other Zr/Ti) increases, only increasing range is different while Zr/Ti is different after polarization. The dielectric constant increasing range of the sample is maximum while Zr/Ti = 52/ 46 and is minimum while Zr/Ti = 54/44, after polarization. The sample (after polarization) with various Zr/Ti was analyzed by XRD(X-ray diffraction) while (Sbo.5 Nb0.5) is 0.02 mol . According to analyzing result, the Table 1
a!
Change of dielectric constant in various ZdTi samples before and after polarization *
ZrITi
52/46
53/45
54144
56/42
€1
1465
1842
2081
1550
€2
1580
1969
2209
1485
(€2 -E,):EI/%
+7.8
+6.9
+6.2
-4.2
*
is dielectric constant before polarization, after polarization EI
€2
is dielectric constant
H w n g X Y et a1 . Properties of La20rDoped PNSZT Piezoelectric Ceramics
sample is composed of tetragonal and rhombohedral phases coexistent. It is obvious that the phase boundary is a certain range, and their quantitative characteristic line intensity of XRD patterns ( I T , I R ) is listed in Table 2. The phase content for tetragonal and rhombohedral phases was calculated by formula fT = I T / ( Z R + IT)and f R = 1 - f T , and is listed in Table 2 . According to Table 2. the tetragonal phase content continuously decreases, and the rhombohedral phase content increases, and while ZrITi increasing. Tetragonal phase content is approximately equal to rhombohedral phase content while Zr/Ti is 54/44. The sample (after polarization) with various Zr/Ti was analyzed by XRD while (Sbo.sNbo.s)is 0.02 mol. The result analyzed was dealt with computer according to Powder X soft ware, and the lattice constants of sample with various Zr/Ti were obtained and listed in Table 3. The lattice constants of sample with various Zr / Ti were determined by means of indexing method . 0 (Sb,,2Nb,,)=0.02
* (Sb,,q,3=0.03
a (Sb,,*q,*)=0.04
-40 -60
d
Various (Sb,,Nb,,)
Fig.4
amount, ZdTi v s . and TMr of
PNSZT
Table 2 Phase composition of various ZdTi sample" 52/46 53/45 54/44 56/42
651 639 628 610
466 543 62 1 672
58.30 54.04 50.27 47.60
41.90 45.96 49.73 52.40
* I T , In are separately quantitative characteristic line XRD intensity, f~, fR are separately phase content for tetragonal phase and rhombohedral phase
Table 3 Lattice constant of various Zr/Ti sample ' ~~
~~
&/Ti
56/42
54/44
53/45
52/46
a T
4.0482 4.1030 4.0727 1.0135 89.703
4.0381 4.1180 4.0696 1.0200 89.682
4.0320 4.1210 4.0604 1.0221 89.673
4.0270 4.1240 4.0550 1.0241 89.669
CT UR
CT/UT
do) *
UT,
CT are tetragonal phase lattice constant,
dral phase lattice constant
UR, a
are rhombohe-
257
In order to decrease inaccuracy, the lattice constant was calculated by XRD patterns data which Bragg angle is close to high angle of 90°[91. According to Table 3 , the lattice constants ( a T , cT, aR, (Y ) of sample are decreased and the axial ratio ( c T / u T ) of sample is increased while Zr/Ti decreasing.
3 Discussion The ionic radius of Sb3' , Nb5+ are separatively rsb3+ = 0.076 nm , rNb5+= 0.069 nm . The ionic radius of ( Sbl/2Nb1/2) is 0.073 nm . The ionic radius of Zr4+ , Ti4+are rzp+ = 0.079 nm, rT++ = 0.086 nm separatively. So, (Sbl,,NbIl2) can enter into (Zr, Ti) site. Sb3+is acceptor ion and entering (Zr, T i ) , NbS+ is donor ion and entering (Zr , Ti ) , and they produce compensation effect, The ratio between electrovalent and ionic radius ( z / r k ) (55.2) of ( Sbl/2Nbl/2)4+ ( z is ionic valance, rk is ionic radius) is more than z/rk (48.8) of (Zr, Ti)4+(Zr/Ti = 56/42 52/46), the bond strength of ( Sb,,,Nbvz) - 0 is stronger than that of (Zr , Ti) - 0 , ( Sbl,2Nbl,2)4+moving temperature is higher than ( Zr, Ti ) moving temperature"]. So, (Sb112Nbl/2)replacing (Zr, Ti) can raise the Curie temperature, increase temperature stable and shift phase boundary to Zr-rich region"]. At the same time, the dielectric constant at room temperature is decreased. The z / r k of ( SblRNbl/,) ion is more than that of (Zr, Ti) ion. The different effect is not neglected when (Sbl,,Nbl,,) amount is high, and they enhance (Zr , T i ) - 0 bond, while coefficient of elasticity (SllE)and K , decreasing. It is difficult for domain to swich, so the dielectric loss decreases, and the mechanical quality factor ( Qm)increases. The experimental result shows that the electric mechanical properties of sample is changed regularly, while ( Sbl/,Nb1,) amount changing. The K , and E of sample are maximum, and Qm of sample is minimum when Zr/Ti is certain amount. The changing law for Tkfr vs Zr/Ti is similar, and the piezoelectric ceramics with minimum Tkfr value may be obtained. In tetragonal phase, spontaneous strain is A Z = c / a - 1 . In rhombohedral phase, spontaneous strain is A Z = id2 - a [ ' ] . In tetragonal phase area, c / a decreases, C Z decreases and then coercive electric field decreases. The motion of domain is easily, the 90 degree domain rotation rate of the sample increases, remainder polarization intensity ( P , ) increases and K , increases, while Zr/Ti in~reasing'~' lo' . The remainder polarization intensity ( P , ) of sample decreases and K , decreases, while c / a decreases greatly. In rhombohedral phase area, the P , an? K , of sample start increas-
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258
JOURNAL OF RARE EARTHS, Vol. 24, Spec. Issue, Dee. 2006
ing and then decreasing while Zr/Ti increasing. Because MPB is tetragonal phase and rhombohedral phase coexistent, the spontaneous polarization orientation increases and K , is maximum at MPB. The maximum value of dielectric constant in MPB is due to D = 0, of which D is the coefficient of dielectric constant thermodynamics unfolding formula"' . MPB is not a line, but is wide componental range, and the wide and narrow of componental range is related to technology factor. There are tetragonal phase and rhombohedral phase coexistent in the componental range. There are big tetragonal and rhombohedral phase coexistent range due to component variation in piezoelectric ceramics prepared by conventional milling mix method, and the componental range for Zr/Ti is 50/50 55/45. MPB is truly component, in which two kinds of phase are equal. The K , and E of the sample are maximum when two kinds of phases are equal, but the K , and E of the sample are small in other phase component ceramics. The changing character of dielectric constant before polarization and after polarization is determined by phase component for various Zr/Ti sample'31. The dielectric constant increases after polarization in tetragonal phase, the dielectric constant decreases after polarization in rhombohedral phase. The dielectric constant of the sample containing more tetragonal phase increases after polarization. In the reverse, the dielectric constant of the sample with more rhombohedral phase decreases after polarization.
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3 . The componental range of tetragonal phase and rhombohedral phase coexist because component variety is big by conventional containing lead piezoelectric ceramic preparation technique. There are maximum piezoelectricity in the ceramics whose tetragonal phase is equal to rhombohedral phase. 4. The dielectric constant of the sample which has more tetragonal phases than rhombohedral phases increases after polarization. The dielectric constant of the sample which has more rhombohedral phases than tetragonal phases decreases after polarization.
References : [ 11 Tecuro Tanaka, et al . Piezoelectric Ceramic Materials
[2]
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Conclusions
The influence of Zr/Ti and ( Sho.sNbo5 ) amount on the structure and properties of La203-dopedPNSZT ceramics having tetragonal phase and rhombohedral phase coexistent ( MPB ) were explored, the conclusions were obtained as follows: 1. The influence of Zr/Ti on the structure and properties of Laz03-doped PNSZT ceramics having tetragonal phase and rhombohedral phase coexistent are big . The lattice constants ( u T , u R , (Y ) of Laz03doped PNSZT ceramics decrease while Zr/Ti decreasing. The lattice constants ( cT, c J u T ) of La203-doped PNSZT ceramics increase while Zr/Ti decreasing. 2 . The influence of (Sb1,,Nbl,,) on the properties of La203-doped PNSZT ceramics is big, while ( Sbl,, Nbllz) additive amount increasing, the mechanical quality factor ( Qm) and temperature stability electric ceramics can be raised.
[6]
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[9]
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