Jpn. J. Appl. Phys. Vol. 41 (2002) pp. 5317–5322
`Part 1, No. 8, August 2002
`#2002 The Japan Society of Applied Physics
`
`Microstructure and Characteristics of Ba(Ti,Zr)O3 Ceramics with Addition of Glass Frit
`
`Chun-Huy WANG
`
`Department of Electronic Engineering, Nan-Jeon Institute of Technology, Tainan, Taiwan 737, R.O.C.
`
`(Received April 8, 2002; accepted for publication April 24, 2002)
`
`Microstructure and characteristics of Ba(Ti,Zr)O3 ceramics are significantly influenced by the addition of 4PbO.B2O3. The
`
`melting temperature of 4PbO.B2O3 was approximately 500
`C, and thus it provides a liquid phase during sintering. At low
`sintering temperatures, the grain growth of Ba(Ti,Zr)O3 ceramics is enhanced by capillary rearrangement and solution-
`reprecipitation from the liquid phase. At high sintering temperatures, exaggerated grain growth of Ba(Ti,Zr)O3 ceramics is
`restrained by the presence of a liquid phase. The spreading liquid can penetrate the solid-solid interfaces. Penetration leads to
`disintegration of the solid and the subsequent rearrangement of fragments. With increasing amounts of 4PbO.B2O3, the
`tetragonal c=a ratio and Curie point temperature increase, but the dielectric loss tangent is depressed. With a suitable amount
`of glass frit and temperature for sintering, the density is enhanced and the values of the planar coupling factor and the poled
`dielectric constant are improved.
`[DOI: 10.1143/JJAP.41.5317]
`KEYWORDS: dielectric and piezoelectric properties, Curie temperature, barium titanate, grain growth, sintering
`
`1.
`
`Introduction
`
`Ferroelectric barium titanate is known as the most
`common oxide in the perovskite ABO3 structure. Insulating
`BaTiO3 is widely used as a dielectric for capacitors because
`of its high dielectric constant.1) In order to increase the
`stability of the dielectric constant against a biasing field and
`to reduce the dielectric loss tangent at low frequencies, ZrO2
`is added.2) In composition Ba(TiyZr1y)O3
`[abbreviated
`BTZ], a very high and broad maximum of the relative
`dielectric constant Kr
`is found at the ferroelectric Curie
`point.3)
`Unfortunately the incorporation of Zr to BaTiO3 raises the
`firing temperature required for the densification of sintered
`samples. In the past, oxides were added as fluxes to lower
`the sintering temperature, such as B2O3, Bi2O3, MgO and
`LiF.4–9) Lead oxide has frequently been used in sintering
`þ2 in the flux is a
`aids for barium titanate ceramics: Pb
`þ2. Inclusion of
`readily soluble isovalent substitute for Ba
`lead oxide in the BTZ ceramics generally improves
`densification, thus sintering could be carried out either with
`lower amounts of glass-former, or at lower temperatures.10)
`In the present work, 4PbO.B2O3 glass frit has been used as a
`sintering aid for
`the densification of
`the BTZ-series
`ceramics. The properties of PbO-based glasses were reported
`by Fajans and Kreidl.11) They found these glasses not only to
`have a low flow temperature, but also to show a high
`polarizability which is helpful
`for polarization of
`the
`ceramic. The melting temperature of the 4PbO.B2O3 was
`
`C, and thus it provides a liquid phase
`approximately 500
`during sintering. Moreover, the PbO-based glasses without
`alkali ions have a low dielectric loss value.12,13) The effects
`of the amount of the glass frit and the sintering temperature
`on the dielectric and piezoelectric properties of BTZ-series
`ceramics are reported.
`
`2. Experimental Procedure
`
`The ceramics used in this study was Ba(Ti,Zr)O3 and the
`glass frit used was 4PbO.B2O3.
`The raw materials used for the frit were reagent-grade
`PbO and B2O3. After mixing, the mixture was placed in an
`
`
`E-mail address: wch70982@ms41.hinet.net
`
`alumina crucible and melted in an electric furnace. Because
`PbO and B2O3 will be lost through vaporization, several
`precautions were taken to ensure compositional accuracy.
`
`
`C–1000
`C and all
`The glass was melted very rapidly at 900
`the melts were held no longer than a total of 30 min at
`
`C, even for
`repeated meltings. Once melting was
`950
`complete, the crucible was removed from the furnace and
`the molten glass was poured into a bucket of cold water.
`After drying, the glass was ground in a mortar and pestle and
`passed through a 325-mesh screen (ASTM size).
`The host Ba(TiyZr1y)O3 powders, with y ¼ 1, 0.96, 0.92
`and 0.88, were formulated and fabricated by conventional
`ceramic technology with reagent-grade BaCO3, ZrO2, and
`TiO2. After weighing, the raw materials were mixed with
`acetone in an alumina ball mill for 4 h. The mixtures were
`
`C for 4 h. The calcined BTZ-
`dried and calcined at 1100
`series powders were mixed with 4PbO.B2O3 glass powder.
`The mixtures of host BTZ-series powders and glass powder
`were homogenized with acetone in the ball mill for 24 h. In
`general, the more homogeneous the additive distribution
`before liquid formation, the more rapid the densification
`during the liquid phase sintering. For this reason,
`it
`is
`common to mill
`the powders longer to increase homo-
`geneity, reduce particle sizes and to break agglomerates.
`After drying, the mixtures were pressed into disk 14 mm in
`diameter and 1 mm in thickness. The samples were covered
`with an alumina crucible and fired under different condi-
`tions. After sintering, the sintered disks were polished and
`silver paste electrodes were fired on both sides. The poling
`technique generally involved immersing the samples in
`silicone oil and subjecting them to a high DC field of 3 KV/
`
`C for 30 min. Twenty-four hours after poling, the
`mm at 100
`dielectric and piezoelectric properties were measured with
`an HP4192A LF impedance analyzer using IRE Stan-
`dards.14)
`In order to determine the crystal structure, crystal system
`and lattice constant,
`the sintered ceramic samples were
`polished and measured at
`room temperature by X-ray
`diffraction (XRD). The free surface of the sintered ceramic
`body was observed using a scanning electron microscope
`(SEM): the mean grain size was calculated by the line
`intercept method.15) The density was measured by the water
`displacement method.
`Exhibit 1034
`IPR2016-00636
`AVX Corporation
`
`5317
`
`000001
`
`

`

`5318
`
`Jpn. J. Appl. Phys. Vol. 41 (2002) Pt. 1, No. 8
`
`C.-H. WANG
`
`Fig. 1. Variation of the measured density of Ba(TiyZr1y)O3 ceramics as a
`
`C for 4 h.
`function of amount of glass frit after sintering at 1150
`
`Fig. 3. Variation of the dielectric constant of Ba(TiyZr1y)O3 ceramics as
`
`C for 4 h.
`a function of amount of glass frit after sintering at 1150
`
`the planar coupling factor of Ba(TiyZr1y)O3
`Fig. 2. Variation of
`
`ceramics as a function of amount of glass frit after sintering at 1150
`C
`for 4 h.
`
`Fig. 4. Variation of the dielectric loss tangent of Ba(TiyZr1y)O3 ceramics
`
`C for 4 h.
`as a function of amount of glass frit after sintering at 1150
`
`3. Results and Discussion
`
`The influence of glass frit 4PbO.B2O3 (0–10 wt%) on the
`properties of Ba(TiyZr1y)O3 ceramics after sintering at
`
`C for 4 h is shown in Figs. 1–4. Figures 1 and 2 show
`1150
`the measured density and the planar coupling factor of BTZ-
`series ceramics as a function of the amount of glass frit,
`respectively. At a constant Zr content,
`the density first
`increases, reaches a maximum point, and then decreases
`with increasing amount of glass frit. The peak value of the
`density is at 7 wt% glass frit for y ¼ 1 and at the addition of
`9 wt% glass frit for y ¼ 0:96, 0.92 and 0.88. Moreover, the
`density of BaTiO3 (y ¼ 1) ceramics has a higher value than
`that of other compositions. The curve of kP has a similar
`tendency to that of density: the maximum value of kP is at
`the addition of 9 wt% for y ¼ 0:92. Figures 3 and 4 show the
`poled dielectric constant "T
`33 and the dielectric loss tangent of
`BTZ-series ceramics as a function of the amount of glass
`
`frit, respectively. The peak value of the dielectric constant is
`at the addition of 2 wt% for BTZ-series ceramics. Regarding
`the dielectric loss tangent,
`it decreases with increasing
`amount of 4PbO.B2O3 because the dielectric loss tangent of
`4PbO.B2O3 frit has a lower value less than 0.005.12,13)
`The effect of glass frit 4PbO.B2O3 (0–5 wt%) on the
`properties of Ba(TiyZr1y)O3 ceramics after sintering at
`
`C for 4 h is shown in Figs. 5–8. Figures 5 and 6 show
`1350
`the measured density and the planar coupling factor of BTZ-
`series ceramics as a function of the amount of glass frit,
`respectively. With the same Zr concentrations, the density
`increases at the beginning and reaches a maximum value and
`then decreases with increasing amount of glass frit. The
`maximum value of density occurs at 0.5 wt% addition of
`(y ¼ 1) ceramics. As the planar
`glass frit
`for BaTiO3
`coupling factor, the peak value of kP is at 1 wt% addition of
`glass frit for y ¼ 0:88 and at 0.5 wt% addition of glass frit
`for y ¼ 0:92, 0.96 and 1. Moreover, the BTZ-series ceramics
`has the largest kp value (0.47) at y ¼ 0:92. Figures 7 and 8
`
`000002
`
`

`

`Jpn. J. Appl. Phys. Vol. 41 (2002) Pt. 1, No. 8
`
`C.-H. WANG
`
`5319
`
`Fig. 5. Variation of the measured density of Ba(TiyZr1y)O3 ceramics as a
`
`C for 4 h.
`function of amount of glass frit after sintering at 1350
`
`Fig. 8. Variation of the dielectric loss tangent of Ba(TiyZr1y)O3 ceramics
`
`C for 4 h.
`as a function of amount of glass frit after sintering at 1350
`
`show the poled dielectric constant "T
`33 and the dielectric loss
`tangent of BTZ-series ceramics as a function of the amount
`of glass frit, respectively. The "T
`33 value decreases with
`increasing amount of glass frit for y ¼ 0:92, 0.96 and 1. As
`the "T
`33 value
`occurs with the dielectric loss tangent,
`decreases with increasing amounts of 4PbO.B2O3 and Zr
`content.
`The variation of the dielectric and piezoelectric properties
`of BTZ-series ceramics with amount of 4PbO.B2O3 glass frit
`can be correlated with the microstructure. The influence of
`the glass frit addition (0 and 2 wt%) on the microstructure of
`
`Ba(TiyZr1y)O3 ceramics after sintering at 1350
`C for 4 h is
`shown in Figs. 9–12. The grain sizes decrease significantly
`with increasing Zr content as shown in Figs. 9(a), 10(a),
`11(a) and 12(a). As the glass frit is added to the BTZ-series
`ceramics (y ¼ 1 and 0.96), the grain sizes of ceramics with
`additives are smaller
`than those of ceramics without
`additives. However, the grain sizes of BTZ-series ceramics
`(y ¼ 0:92) with additives are only slightly smaller than those
`without
`additives. Conversely, BTZ-series
`ceramics
`(y ¼ 0:88) with additives has larger grain sizes than that
`without additives. Figure 13 shows the grain sizes of BTZ-
`series ceramics as a function of the amount of glass frit after
`
`C for 4 h. BaTiO3 ceramics has larger
`sintering at 1150
`grain sizes than other compositions. With the same Zr
`content, the grain sizes of BTZ-series ceramics increase with
`increasing amount of glass frit. Figure 14 shows the grain
`sizes of BTZ-series ceramics as a function of the amount of
`
`C for 4 h. As the glass frit is
`glass frit after sintering at 1350
`added to BTZ-series ceramics, the grain sizes of BTZ-series
`(y ¼ 1, 0.96 and 0.92) ceramics decrease with increasing
`amount of glass frit, but those of BTZ-series (y ¼ 0:88)
`ceramics increase with increasing amount of glass frit.
`From the above results, it is evident that 4PbO.B2O3 glass
`frit can reduce the sintering temperature and improve the
`properties of BTZ-series ceramics. The crystalline phase was
`confirmed by XRD to be a single phase with a perovskite
`structure. Figure 15 shows the Curie point
`temperature
`(determined electrically) of the BTZ-series ceramics as a
`
`C
`function of the amount of glass frit after sintering at 1350
`
`the planar coupling factor of Ba(TiyZr1y)O3
`Fig. 6. Variation of
`
`ceramics as a function of amount of glass frit after sintering at 1350
`C
`for 4 h.
`
`Fig. 7. Variation of the dielectric constant of Ba(TiyZr1y)O3 ceramics as
`
`C for 4 h.
`a function of amount of glass frit after sintering at 1350
`
`000003
`
`

`

`5320
`
`Jpn. J. Appl. Phys. Vol. 41 (2002) Pt. 1, No. 8
`
`C.-H. WANG
`
`Fig. 9. Microstructure of BaTiO3 ceramics with different 4PbO.B2O3
`
`additions [(a) without doping and (b) 2 wt%] after sintering at 1350
`C for
`4 h.
`
`Fig. 10. Microstructure of Ba(Ti0:96Zr0:04)O3 ceramics with different
`4PbO.B2O3 additions [(a) without doping and (b) 2 wt%] after sintering
`
`C for 4 h.
`at 1350
`
`Table I. Lattice constant of Ba(TiyZr1y)O3 as a function of amount of
`
`C for 4 h.
`4PbO.B2O3 after sintering at 1350
`
`Composition
`
`y ¼ 1
`
`y ¼ 0:96
`
`y ¼ 0:92
`
`y ¼ 0:88
`
`0 wt%
`a ¼ 3:995
`c ¼ 4:029
`c=a ¼ 1:009
`a ¼ 4:002
`c ¼ 4:031
`c=a ¼ 1:007
`a ¼ 4:014
`c ¼ 4:035
`c=a ¼ 1:005
`a ¼ 4:029
`c ¼ 4:035
`c=a ¼ 1:001
`
`2 wt%
`a ¼ 3:997
`c ¼ 4:036
`c=a ¼ 1:010
`a ¼ 4:004
`c ¼ 4:037
`c=a ¼ 1:008
`a ¼ 4:016
`c ¼ 4:040
`c=a ¼ 1:006
`a ¼ 4:031
`c ¼ 4:040
`c=a ¼ 1:002
`
`7 wt%
`a ¼ 3:999
`c ¼ 4:046
`c=a ¼ 1:012
`a ¼ 4:006
`c ¼ 4:047
`c=a ¼ 1:010
`a ¼ 4:018
`c ¼ 4:049
`c=a ¼ 1:008
`a ¼ 4:033
`c ¼ 4:050
`c=a ¼ 1:004
`
`for 4 h. Table I shows the effect of the glass frit addition on
`the lattice parameter in BTZ-series ceramics after sintering
`
`C for 4 h. In the Ba(TiyZr1y)O3 solid solutions,
`at 1350
`both c and a (the lattice constants) increase as the Zr content
`is increased, but the c=a ratio decreases. Neirman13) also
`reported that the lattice constants of Ba(Ti, Zr)O3 ceramics
`increase with incorporation of Zr. This is expected since the
`þ4
`þ4 (0.87 A) is larger than that of Ti
`ionic radius of Zr
`
`(0.68 A) which it replaces. With increasing Zr content, the
`average radius of the B-site expands which leads to a higher
`fraction of increase in the a-axis than in the c-axis, and the
`average displacement of B-site ions along the polar axis
`decreases. This causes the tetragonal c=a ratio and the Curie
`temperature of BTZ-series ceramics to decrease.
`In microstructural observations of BTZ-series ceramics,
`the incorporation of Zr is found to inhibit the grain growth.
`This can be explained on the basis of kinetic arguments. The
`grain growth is associated with mass transport from the
`location of a higher solubility/curvature to the location of a
`lower solubility/curvature. During mass transport, which
`takes place via diffusion, distance is important. The larger
`the transport distance (a larger amount of liquid phase), the
`smaller the area to length ratio (A=x) between two dissimilar
`particles, and the smaller the mass flow per time unit as well
`as the grain growth. On the other hand, the heavier and
`þ4/Ti
`þ4, the smaller the
`larger the species transported, i.e., Zr
`diffusibility at the same ionic charge. These are the main
`arguments which explain the course of average grain size vs.
`the composition in Fig. 13. Regarding the effect of the
`4PbO.B2O3 glass frit on the microstructure of BTZ-series
`ceramics, grain growth is enhanced by the presence of a
`
`C), but
`liquid phase under a low sintering temperature (1150
`it is restrained (except at y ¼ 0:88) by the presence of a
`
`C). On
`liquid phase at a high sintering temperature (1350
`formation of a liquid phase, there is a rearrangement of
`
`000004
`
`

`

`Jpn. J. Appl. Phys. Vol. 41 (2002) Pt. 1, No. 8
`
`C.-H. WANG
`
`5321
`
`Fig. 11. The microstructure of Ba(Ti0:92Zr0:08)O3 ceramics with different
`4PbO.B2O3 additions [(a) without doping and (b) 2 wt%] after sintering at
`
`C for 4 h.
`1350
`
`Fig. 12. The microstructure of Ba(Ti0:88Zr0:12)O3 ceramics with different
`4PbO.B2O3 additions [(a) without doping and (b) 2 wt%] after sintering at
`
`C for 4 h.
`1350
`
`particles to allow more efficient packing. There is a solution
`of smaller particles with the growth of larger particles by
`material
`transfer
`through the liquid phase during the
`sintering process. When the liquid phase penetrates between
`particles,
`the pressure at
`the contact points leads to an
`increased solubility such that there is mass transfer away
`from the contact areas, so that the centers of the particles
`approach one another, resulting in shrinkage. Hence, the
`grain sizes of BTZ-series ceramics increase with increasing
`
`C).
`amount of glass frit at a low sintering temperature (1150
`
`C), exaggerated grain
`At a high sintering temperature (1350
`growth occurs for BaTiO3 ceramics. During the sintering
`process, when the boundary curvature and the driving force
`for boundary migration are high, pores are often left behind.
`The grain growth processes must be actively prevented in
`order to obtain complete densification. 4PbO.B2O3 addition
`to the BTZ-series ceramics (y ¼ 1, 0.96 and 0.92) is a
`satisfactory way to eliminate pores while also inhibiting
`grain growth.
`The characteristics of BTZ-series ceramics vary with
`different Zr contents and amounts of 4PbO.B2O3 glass frit;
`higher sintering temperatures lead to higher densities.
`However, higher Zr contents result in lower densities. When
`a suitable amount of glass frit was added to BTZ-series
`ceramics, the porosity decreased and the density increasesd.
`However, an excess of glass frit will decrease the density of
`
`Fig. 13. Variation of the grain sizes of Ba(TiyZr1y)O3 ceramics as a
`
`C for 4 h.
`function of amount of glass frit after sintering at 1150
`
`BTZ-series ceramics owing to the theoretical density of
`glass frit being less than that of BTZ-series ceramics. It was
`þ4 by Zr
`þ4 ion
`known that a substantial replacement of Ti
`causes depression of the Curie point but a rise in the
`orthorhombic-tetragonal and rhombohedral-orthorhombic
`
`000005
`
`

`

`5322
`
`Jpn. J. Appl. Phys. Vol. 41 (2002) Pt. 1, No. 8
`
`C.-H. WANG
`
`have a low dielectric loss value11) and 4PbO.B2O3 has the
`dielectric loss value below 0.005. This causes a decrease in
`the dielectric loss with increasing amount of glass frit.
`
`4. Conclusions
`
`The 4PbO.B2O3 flux appears to be a densification
`promoter for BTZ-series ceramics. Under low sintering
`temperatures, the grain growth of BTZ-series ceramics was
`enhanced by capillary, rearrangement and solution-repreci-
`pitation of the liquid phase. At high sintering temperatures,
`exaggerated grain growth of the BTZ-series ceramics was
`restrained by the presence of a liquid phase. Subsequently,
`the liquid penetrates the grain boundaries and causes
`fragmentation. Particle penetration and fragmentation are
`the main reasons for the lowering of the grain growth rate.
`With increasing amount of the 4PbO.B2O3, the tetragonal
`c=a ratio and the Curie point temperature of BTZ-series
`ceramics are raised. The glass frit addition also has
`significant effect on the dielectric and piezoelectric proper-
`ties of BTZ-series ceramics. With suitable additions of glass
`frit, the sintering temperature and the porosity are decreased
`and the density is increased. In general, raising the density is
`relative to improving the properties. However, the theore-
`tical density, dielectric loss tangent and the dielectric
`constant of 4PbO.B2O3 are smaller than those of BTZ-
`series ceramics, and these properties are depressed with the
`addition of excess 4PbO.B2O3.
`
`Acknowledgements
`
`The author would like to acknowledge the financial
`support of the National Science Council (under the contract
`NSC-89-2626-E-232-003) of the Republic of China.
`
`1) F. Brown: IRE Trans. Component Parts 2 (1959) 238.
`2) T. R. Armstrong, L. E. Morgens, A. K. Maurice and R. C. Buchanan:
`J. Am. Ceram. Soc. 72 (1989) 605.
`3) D. Hennings, A. Schnell and G. Simon: J. Am. Ceram. Soc. 65 (1982)
`539.
`4) G. C. Nicholson: J. Am. Ceram. Soc. 48 (1965) 525.
`5) K. R. Chowdry and E. C. Subbaro: Ferroelectrics 37 (1981) 689.
`6) B. E. Walker, Jr., R. W. Rice, R. C. Pohanka and J. P. Spann: Am.
`Ceram. Soc. Bull. 55 (1976) 274, 284.
`7) P. B. Amin, H. U. Anderson and C. E. Hodgkins: U.S. Patent 4082906
`(1978).
`8) G. Desgardin, I. Mey, B. Raveau and J. M. Haussonne: Am. Ceram.
`Soc. Bull. 64 (1970) 564.
`9) Y. Tsur, A. Hitomi, I. Scrymgeour and C. A. Randall: Jpn. J. Appl.
`Phys. 40 (2001) 255.
`I. Burn: J. Mater. Sci. 17 (1982) 1398.
`10)
`11) K. Fajans and N. J. Kreidl: J. Am. Ceram. Soc. 31 (1948) 105.
`12) W. D. Kingery, H. K. Bowen and D. R. Uhlmann: Introduction to
`Ceramics (Cambridge, Massachusetts, 1975) 2nd ed., p. 941.
`13) S. M. Neirman: J. Mater. Sci. 23 (1988) 3973.
`IRE Standards on Piezoelectric Crystals: Measurement of Piezo-
`14)
`electric Ceramics 1961, Proc. IRE 49 (1961) 1161.
`15) T. Senda and R. C. Bradt: J. Am. Ceram. Soc. 73 (1990) 106.
`
`Fig. 14. Variation of the grain sizes of Ba(TiyZr1y)O3 ceramics as a
`
`C for 4 h.
`function of amount of glass frit after sintering at 1350
`
`temperature of Ba(TiyZr1y)O3
`Fig. 15. Variation of the Curie point
`
`ceramics as a function of amount of glass frit after sintering at 1350
`C for
`4 h.
`
`transition temperature.3) This means that
`the tetragonal,
`orthorhombic and rhombohedral phases become stable at
`room temperature. This causes a rise in the ferroelectric
`polarization at room temperature so that the piezoelectric
`coupling factor is enhanced. The glass frit 4PbO.B2O3 also
`has a significant effect on the dielectric and piezoelectric
`properties of BTZ-series ceramics. With a suitable addition
`of glass frit, the values of kP and "T
`33 of BTZ-series ceramics
`"T
`33,
`by
`adding
`excess
`are
`decreased,
`particularly
`4PbO.B2O3. The PbO-based glasses without alkali
`ions
`
`000006
`
`