Structure and Properties of High Piezoelectric ...

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Fet.roelec~rics, 1999, Vol. 224. pp. 137-144 Reprints available directly from the publisher Phntocnpylng permitted by license only

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Structure and Properties of High Piezoelectric Coupling Pb(B' 1/2Nb1/2)03-PbTi03 Binary Systems ANDRIS STERNBERGa, LEONIDS SHEBANOVSa, JOHN Y. YAMASHITAb, MAIJA ANTONOVAa, MARIS LIVINSHa and

IVAN SHORUBALKOa ahtitUte of Solid State Physics University of Latvia, Riga LV-1063, Latvia; and bToshiba Corporation, Kawasaki-city 210-8501, Japan (Received August 24, 1998: In final form September 22, 1998) The (l-x)Pb(Lul/2 Nb1,,)03-xPbTi03 and (l-x)Pb(ErlI2Nbl,z)03-xPbTi03 binary systems have been obtained, the structure and properties of which are studied. The unit cell of erbium niobate (PErN) is described as pseudomonoclinic of orthorhombic Bmm2 symmetry: a=c=4.2161 A; b=4.0869 A; p=90.55' and composition is characterized with antiferroelectric phase transition at 305'C. The PErNT system has the morphotropic phase region extending over the x=0.4-0.6 interval. In PLuNT ceramics system the pseudomonoclinic phase strncture Bmm2 extending over the O k a . 3 8 interval becomes pseudocubic at x= 0.2. The morr' concentrations (1.0 2 x 2 0.49) photropic region is spread over 0.38< x < 0.49; at higher F the structure transfers to the tetragonal P4mm phase. The maximum values of the electromechanical coupling coefficients k,=0.66, k,=0.48, k, ,=0.35 were attained in compositions PLuNT 59/41 near the rnorphotropic phase boundary.

Keywords: piezoelectric ceramics; binary systems; lutecium niobate; erbium niobate; relaxor; phase diagram; dielectric and electromechanical properties

INTRODUCTION Multicomponent

piezoelecetric

perovskites

including

Pb(B',B")03

compounds, mainly relaxors and lead titanate PbTiO3 (PT), e.g., PSN-PT"',

PSN-PMN-PT[", PMN-PT'.'-'], PST-PT[61, PZN-PSN"', PYbNT'*], PMN-

[565]/137

138/[566J

ANDRIS STERNBERG et al.

PMT-PTL9' PNN-PT-PZ"" electromechanical

are of particular

(piezoelectric,

interest due to high

electrostrictive)

characteristics

and,

therefore, promising for application in electronics, ultrasound transduction, acoustic sensing, microelectromechanical systems as well as for studies and


further understanding of the physics of relaxors [3-51. An essential advantage compared to conventional PZT compositions is the considerable ease of growing complex perovskite single crystals

"1-'31.

Ultrahigh electromechanical coupling and piezoelectric coefficients have been reported in PZNT(x=0.08 PT) crystals- k3p0.9, d33 L 2000 PC/"'~'. The

solid

solution

systems

(1 -x)Pb(Lu1/2N b 1 / 2 ) 0 3 -xPbTiO3

and

(I-x) Pb (Erl/2N b l ~ ) 0-xPbTiO-, 3 (further abbreviated as PLuNT and PErNT) were examined with the aim to investigate structural, dielectric and piezoelectric properties of ceramics, especially in the morphotropic phase boundary (MPB) region.

EXPERIMENTAL To obtain the solid solution series both conventional mixed oxides route and

the wolframite precursor method were used. In case of the PLuNT system the latter provided better results, but in case of the PErNT system the mixed oxide techniques appeared to be more successful: in the 30-80mol.% concentration interval of PbTiO3 it provided substitutional solid solutions. The technological parameters and distinctions of PLuNT and PErNT synthesis as well as specimen testing are given in the flow sheet (Fig. 1). Crystallographic studies were made by X-ray diffraction maxima 200, 220, 222 analysis using a DRON-UMI diffractometer with Co K, radiation, and Fe

0 filter. Dielectric permittivity

and loss were measured using a HP4284

LCR instrument, the piezoelectric measurements were made on a HP4 I94 impedance analyzer.

STRUCTURE AND PROPERTIES OF l'b(B' ,,,Nbl,,)03-PbTi03

PErNT

PLuNT


PbO. Lu~OI, Nb205, T102~99.92

(Lul/2Nb,,?)Oi- 1250°C I h PbTiOl - 800°C I h P ~ ( L U ~ / ~ N ~ I800°C , ~ ) O II -h

930"- I I Sd'C 2 5-6 5h, 25 MPa

[567]/139

WEIGHlNG

PbO, Er20,, Nb205.TiO, 99,9%

850'' 2h

HOT-PRESSING X-ray analysis, density, rnicrostruclure

950"- 1 100°C 10-16h. 25 MPa

RESULTS AND DISCUSSION Ceramic ProDerties

To compensate the loss 1 wt.% of excess PbO in case of PLuNT was added to the mixture. However, this turned out not to be the optimum amount being specific to each of the compositions. Remaining PbO, on the other side, is

140/[568]

ANDRIS STERNBERG et al.

responsible for poor polarization (leaky hysteresis loops) and lower electromechanical coupling. Specific resistance of the PLuNT samples at room temperature is 3.1OU-1O9 R.m. At poling temperatures of 120 -130°C it


decreases to

lo7 a . m .

Ceramic samples of PLuNT obtained from compositions with I wt.% of excess PbO have a dense structure and comparatively large grains of the average size of 5-6 pm while many small pores and average size of grains 1-2 pm are characteristic to samples obtained from stoichiometric mixtures. Ceramics density p gradually decreases if PT concentration increases as expected from the density values calculated from X-ray data: for "end" compositions PLuN and PT Pcalculated is 9.1 g/cm' and 7.9 g/cm3, correspondingly. In case of PErNT system the amount of excess PbO added was even higher up to 3 wt.% because of a higher calcining temperature (Fig.1) and, therefore, higher volatility of PbO was expected in case of PErNT compared to PLuNT.

Phase Diagram Pure lutecium niobate (PLuN) has a pronounced long-range order in the B sublattice (the X-ray diffraction pattern suggests a superstructure) and a pseudomonoclinic (psd-M) cell with linear parameters a=c=4.150 A, b=4.119

A

and angle p=90.43' (Fig.2a,b). The space group of PLuN and compositions at small x is Bmm2 and the true unit cell is orthorhombic; the orthorhombic

(nu& bonh; Coflh) and pseudomonoclinic (arb,@) sets of parameters are associated by relations: &flh=2a sin @/2;bonh=2a cos @/2;conh=b. With the increase of x (the concentration of PbTiO3) the long-range order in the B sublattice disappears - assuming the 1: 1 ordering the I % Y,

/I~oo ratio

changes gradually from 0.919 to 0.054 as x is changed from 0 to 0.3. An intermediate phase between the antiferroelectric PLuN and ferroelectric PT is expected as in the case of PZT system at small concentrations of PT (x