INVESTIGACiÓN REVISTA MEXICANA DE FíSICA 44 (1) 65-67 FEBRERO 1998

Obtention of a non stoichiometric PMN-PT ferroelectric system

A. Fundora, J. Ponelles, A. Penlón, am! F. CalderónDepartamento de Ciencia de Materiales. U"i\'ersidad de la Habana

Habana 10400, Cnba

J.M. Siqueiros, R. Machorro, and O.A. HiralaInstituto de F(sica, Unl\'ersidad Nacional Aur6nonw de México, Laboratorio de Ensenada

ApartGl/o postal 2681,22800 Ensenada, Raja Califomia, Afexico

Recihido el 23 de agosto de 1996; aceptado el 21 de abril de 1997

Thc ()otcntion of a non stoichiomctric PMN-PT system has been studicd. Thc int1ucncc of differem PhZr03 atmospheres in [he sinteringproccss of 3(1 - x)Pb(Mg1/3Nb2/3)03 + xPbli03 (PMN-PT) solid solution has beco investigalcd and rncasured by thermoelectric analysisal I kilI.. Yalucs lower than those for [he stoichiometric PMN.PT systcm have hccn ohtained for Te. X-ray diffraction (XRD) was perforrnedin the samples for structural analysis and phase identification.

K('.'r"words: Perovskite. ferroelectric

Se presenta el estudio de la obtención de un sistema PMN.PT no estequiométrico. Se investiga la influencia de diferentes atmósferas dePbZrOJ en el proceso de sinterizado de la solución sólida de 3(1 - x )Pb(Mg1f.1Nb:l/3)03 + xPblí03 (PMN-P1) y se caracterizJ medianteanálisis termocléctico a 1kHz. Se reportan valores de la temperatura crílica Te inferiores a los obtenidos para el sistema estequiométrico dePMN-JYf. Se utilizó la técnica de difracción de rayos X (XRD) para análisis estructural e identificación de fases en las muestras.

Descriptores: Perovskita. ferroeléctrico

PACS: 77.84.-<; 77.80.Bh, 77.84.Dy

I. Introduction

Relaxors hased on lhe perovskile 3(1 -x)Ph(Mg1/3Nb'/3)03+xPbTi03 solid solutions exhibit excellent dielectric prop-crties ano are of current ¡nterest for multilayer capacitorfabrication [IJ. The preparation of a rure pcrovskite phaseof PMN by the conventional mixed oxides methad withoutthe formation of an associated pyrochlorc phase is a verydiflíeult lask. DuelO the low dieleelrie eonslanl of the py-roehlore phase [2], Ihe dieleelrie eonslanl of Ihe sample wilIdecre3.'\e with respect to that al' apure perovskite. Swartzand Shroul [3) developed a melhod lo proeess pure PMNperovskile hy preealcining the mixlure of MgO and Nh,O"lo form MgNh,06 whieh has a eolumhile slruelure and Ihenreaeling il wilh PbO lo from PMN. The addition of exeessMgO to PMN-hased eeramies has been shown [4-{j] lo havea beneficial cffeet to reduce and evcn climinate the presenceof Ihe pyroehore phase.

The aim of this work was to obtain a non stoichiomet-ric PMN-fYf system by the ceramic convcntional method us-ing columbite precursor method with 5% mole excess MgOand rneasurc its properties. The atmosphcre intluence in Ihesinlcring proccss has been studied by thcrmoelectric analysis(TEA) and XRD.

2. Experimental Procedure

The non sloiehiomelrie eeramies 3(1 - x)PMN + xPT (x =0.1-;).4) were prepared hy lhe slandard eeramie melhod. Thef1rst slagc was the formation of columbite MgNb206 with 5%mole exeess MgO [í]. The samples were sinlered al 12000Cfor 2h under different concentrations of PbZr03 as atmo-sphere. The effeet of the differenl preparation atmosphereson the dielectrie propcrties wa...•studicd at 1kHz using a BM509 RLC meler eonlrolled hy a personal eompuler. The heat-ing rate was mainlained al IOC/min.

3, Result~ and Discussion

Figure I shows tcmpcraturc dependen ce of the dielectric per-mittivity for;t = 0.3 and 0.4, respcctively. The maximumvaluc of the dieleetric pcrmittivity inereases with the PbZr03concentration in the sintering atmosphere as it is varied from0.5 lo 2.5 grams bUl deereases slightly for 3.0 g of PbZr03.Thesc results agree wilh similar rcports on stoichiometricPMN:PT eeramies where lhe exeess or defieil ofPbO leads lo(he formation of a pyrochlorc phase. Analogous results wcreohtaincd ror camposilions with .C = 0.1, 0.2

Table 1 shows the values of the maximum dielcctric con-stant [max amI the transitioll temperature (Te) forsintered

66 A. FUNDORA ET AL.

TABLE l. Composition (x% ofP1), Te, E"max,lattice constants and ealculated deformation parameter ofnon stoichiometric PMN:PT systems.

x (%PT) To(°C) cmax a (A) e (A) (a'e)'/' (A) Deformation parameter, Ó

0.1 (3%) 8 I1 000 4.042 4.045 4.042 0.000742

0.2 (8%) 27 16 000 4.038 4.052 4.042 0.002470

0.3 (12%) 57 18 000 4.035 4.055 4.041 0.003460

0.4 (18%) 91 26000 4.030 4.057 4.038 0.004700

ooסס,-.- o 5g?l)lrO,-.-1.0g PlIZrO,

-.- 2 5g Pb.UJ,_l(_ 3.0g F'bZrO,

ooסס2

E

""""ooסס,

'''''''oo

-.-O.5~Pb.ZrO,

-.-lOIlPl:>ZrO,-e-25I1PbZrO,

-x-300Pl:>ZlO,

200

>2"""

."""

100 150

T(C)

200

w 00FIGURE l. The temperature dependence of the dielectric constant for (a) x = 0.4 and (b) x = 0.3.

TABLE 11. Composition ($% of P1) and corresponding Te of stoi.chiometric PMN:PT systems.

X (% PT) T,3 158 4014 7022 120 ,

PT,

samples wilh a 2.5 g almosphere. As lhe titan ate eontenl isdecreased in the samples, Te takes Iower values; these resultsagree with similar reports in stoichiometric PMN:PT ceram-ies but. for eaeh eomposition. (x = 0.1-D.4). the eorrespond-ing T, is a little lower than that oflhe stoiehiometrie PMN:PTsystem, since the amooot of PT by pereent is very small COffi-pared wilh PMN. Por instanee. when x = 0.1 it will be 3%mole of PT inlo the PMN. Table Il shows the lransition tem-perature values of the stoichiometric PMN:PT systcm in theanalyzed concentration range.

X-ray diffraetion analysis ofthe sample was perforrned ina HZG-4 universal diffraetomenler using the Ka Coball linescanning continuously al 2°/min in a 20°_70° range for 28.The X-ray diffraetion patterns of 3(1- x)PMN +xPT mate-rials (x = 0.1-D.4). represented by samples PT1• PT2. PT,and PT4 respectively. are shown in Fig. 2. In lhese patterns.the absence of the (222) eharaeteristie diffraetion peaks oflhe pyroehlore phase is eonfirmed. as opposed lo those of thesolid solution reported by Wang and Sehulze [7]. However.we must point out that under the conditions prevailing during

PT,

25 30 35 40 45 50 55 W 65 m2B (degrees)

Figure 2. X-ray diffraction patterns of 3(1 - x)pMN +xP'T mate-rials sintered at 1200°C for 2 h, with a 2.5 g PbZr03 atmosphere.

(x = 01 {PT,).r = 0.2 {PT,).r = 03 (PT,},x = 0.4 (PT.))

the measurements, it was impossible to detect the presenceof a phase under 5% of relative abundance. From the X-rayresults reported in Pig. 2. a systemalie shift toward larger an-gles of the diffraetion peaks was determined as the PT rel-ative conccntration was increased. In Fig. 3 the shift in theangular position of the (112) peak wilh the PT can be ob-served for all studied compositions with an estimated uncer-tainty in the position of the peak of 28err = 0.04°. Fromthis shift. an inerease of the letragonality of lhe eell withthe PT concentration can be qualitatively inferred. Accord-ing lO the pereent eontent of PT on PMN. samples PT1•PT 2 and PT 3 should be pseudo-cubic but our samples exhibit

Rev. Mex. Fís. 44 (1) (1998) 65-67

OBTENTION OF A NON STOlCHlOMETRIC PMN.PT FERROELECTRIC SYSTEMbSqS ,--------------,

67

n M8~

11 M.!W

~A M7S

M10

o

o

o

o "'"

8 OOOJ

"'"'00'oono

2 ~ 6 8 10 12 14 16 18 W 22 ~PT(%1

Figure 3. Dependence of the position of the (112) peak with the PIconcentratíon.

010 01' oro 02' OM 0" O~PbTiOJ (%mo1)

Figure 4. The compositional dependence of the deformalion param-eler b.

is also reported against the PT contenl. This is caHed the de-forma/ion parame/er Ó by Fesenko e/ al. [11].

When the deformation parameter is different from zero(ó l' O) these materials are ferroclectric in the tetragonalphase and are paraelectric in the cubic phasc also preseot OUT

materials. On the other hand, !he pseudo.cubic PMN ma.[crials show remarkable ferroelectricity al low temperaturcs(T < - J00e) and crystals with cubic symmetry exhibit ó = o.

a tetragonal structurc. This results disagrecs with those rc-ported by Choi e/ al. [8]. Shroul el al. [9J and Ho el al. [10Jwho claim lbat stoichiometric PMN:PT with Ihese composi.tions has a pseudo.cubic struclure. In Table 1, high values fortmax [or a1l compositions as well as an ¡ncrease in £max withPT concentration can be observed. This faet strongly sup-ports the non existence of the pyrochlore phase since, for thePMN based syslems. the dielectric constant decreases withthe pyrochlore conccntration. The lattice parameters c. a andceH volume (a2c) are caJculated from the XDR paneros andare shown in the Table 1. In the same table. a ncw parameterrelated to lhe lanice constanl of the tetragonal crystal struc.ture, defined according lO:

ó=[c - (a2c)1/3]

(a2c)'/3 (1)

Finally, Fig. 4 shows the compositional dependence of thedeformation parameter with the Icad t¡tanate molar concen~tration.

4. Conclusion

The non stoichiometric PMN.PT system was obtained by thecolumbite precursor method with 5% mole excess of MgO.These materiaIs have apure perovskite phase which is evi-denced by X-ray diffraction analysis and lhe samples showgood ferroelectric properties. Dielectric anaiysis suggeststhat the decrease in the dielectric constant for the higher PTconcentrations is attributed lo presence of a pyrochlore phase.The deformation parameter Ó, is found lo be very suitablelo describe the compositional dependence of the ferroelec-trie properties. Thc transition temperatures found for the nonstoichiometric PMN:PT system are lower lban those of lbestoichiometric PMN:PT system with lhe same amount of PTinPMN.

Acknowledgments

One of the authors, JMS, wishes to lhank lbe Consejo Na.cional de Ciencia y Tecnologfa of México and DGAPA.UNAM, for partially supporting lhis work lhrough grants4143E and INIÓ8995. respectively.

t. M. Lejeune and J.P.Boilol, Phys .. Colloq. CI,Supl. 2,47 (1986)Ct.895.

2. T.R. Shroul and S.L. Swartz.Mata Res. Hull. 18 (1983) 663.3. S.L. Swartz and T.R. ShroUI,Mata Res. 8ull. 17 (1982) 1245.4. K. Furukawa, S. Fujiwara. and T. Qgasawara, Proceeding o/

the Japan-u.s. 5tudy Seminar on Dielectric and PiezoelectricCeramics P. (1982) T-4.

5. S.L. Swatrz. T.R. ShroUl. W.A. Schulze. and L.E. Cross, 1. Am.Ceram. Soco 54 (t984) 3t 1.

6. E. Goo. T. Yamamoto. and K. Okazaki. 1. Am. Ceram. Soco 69(1985) e-188.

7. H.e. Wang and W.A. Schulze, 1. Am. Ceram. Soco 73 (1990)825.

8. S,W. Choi. T.R. Shrout, S.J. Jang, and A.S. Bhalla. Ferro-electrics 100 (1989) 29.

9. TR. Shroul. Z,P. Chango and S. Markagraf. Ferroe/ect. Lelt. 12(1990)

10. J.e. 110. K.5. Liu. and I.N. Lin. 1.. Mat. Se. 28 (1993) 4497.

11. E.G. Fesenko, V.S. Felip'ev, and M.r. Kupriyanov, SOy. Phys.Solid State 11 (1969) 366.

Rev. Mex. Fis. 44 (1) (1998) 65-67