Some effects of different additives on dielectric and

1
? ? ? ? ?

• Some effects of different additives on dielectric
  and
• piezoelectric properties of (Bi½Na½)TiO3 - BaTiO3
  
• morphotropic-phase-boundary composition

2
Abstract

• Microstructure, dielectric and piezoelectric of
  (Bi1/2Na1/2)TiO3 - 6BaTiO3 doped with Nb5 ,
  Co3 ,
• or La3 were studied for a candidate as
  lead-free pizoelectric ceramics.
• The doping with Co3 enhanced piezoelectric coeff
• -icient(d33) and lower dielectric loss.
• The Co3 doped system's intermediate phase
  transition almost disappeared.

3
Introduction 1.

• Bismuth sodium titanate, (Bi1/2Na1/2)TiO3
• ? an attractive lead-free A-site
  complex-perovskite for
• high-Tc ferroelectric relaxor material.
• The BNT-based ceramic materials are of interests
  as new
• candidates to replace the widely used
  lead-contented
• perovskite materials.
• ? the free control of sintering atmosphere
  and lack of lead
  
• pollution during the process of
  preparation.
• To improve its properties, several solid
  solutions of BNT
• with PbTiO3 SrTiO3 , (SraPbbCac)TiO3 ,
  La2(TiO3)3 , CaTiO3
• and BaTiO3 have been studied.

4
Introduction 2.

• Among these BNT-based system, (Bi1/2Na1/2)TiO3 -
  BaTiO3
• (BNT)is more arresting.
• The aim of this paper ? to investigate the
  effects of single and cooperative substitution on
  (Bi1/2Na1/2)TiO3 - 6BaTiO3
• system by studying the dielectric and
  piezoelectric propert
• -ies of (Bi1/2Na1/2)TiO3 - 6BaTiO3 doped
  with (1 at.)La 3,
• (1 at.)Nb5 or (1 at.)Co 3.

5
Experiment 1.

• The conventional ceramic fabrication technique
  was used to prepare these ceramic samples.
• The high purity of starting metal oxide or
  carbonate powders, such as Bi2O3, Na2CO3, BaCO3,
  TiO2, Nb2O5, Co2O3 and La2O3
• were used.
• The powders of these raw materials ? in ethanol
  with carnelian
• balls by ball-milling for 12 h ? calcined
  at 1000 ? for 2 h ?
• were ground and ball-milled for 24 h into
  the fine powders and were pressed into discs,
  16.4 or 12 mm in diameter and 1 mm in
• thickness ? some of these small discs as
  the samples were sintered at 1160-1200 ? for 2 h
  in an air atmosphere.
• All samples were sintered at the temperatures
  leading to the maximum relative densities.

6
Experiment 2.

• FESEM(field emission scanning electron
  microscope)
• ? The surface micrograph of sintered
  samples.
• Atomated diffractometer
• ? X-ray diffraction patterns.
• Multifrequency LCR meter
• ? Temperature dependence of dielectric
  constant and loss tangent
• Piezo d33 meter
• ? The piezoelectric charge coefficient

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Results and discussion 1.

• Its not necessary to control the atmosphere
  during the sintering process of these ceramics ?
  the limited evaporation of the raw
• materials, which is not the case with
  conventional PZT or PZT-
• based ceramics.
• X-ray diffraction data at room temperature ? that
  all of the
• samples have a structure of rhombohedral
  phase.
• Figs 1 and 2 show temperature dependences of
  dielectric
• constant e 33T and tan d of all the
  samples, respectively.
• All samples that show the curie points in Figs. 1
  and 2 are
• shifted to higher temperatures ? it can be
  thought that the
• additives have influenced the crystal
  lattices.

8
Results and discussion 2.

• For all BNBT6 samples with additives, the
  dielectric constant is higher than BNBT6 at room
  temperature and the e 33T temperature curves of
  the compositions exhibit strong dielectric
  dispersion with the increasing temperature.
• ? the diffuse phase transition
• BNBT system is a typical relaxation
  ferroelectric with A-sit
• complex ions .

9
Results and discussion 3.

• The pure BNBT6 and BNBT6 doped with La3 or Nb5
  ? a sharp increase of permittivity near about
  100?? the tendency of the increase becomes slow
  and the curve begins to broaden.
• "a shoulder" ? intermediate phase transition.
• the temperature region between the shoulder and
  Tmax ? an anti-ferroelectric phase .

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Results and discussion 4.

• The BNBT6 systems to which Co3 is added, "the
  shoulder" almost dis-
• appeared.
• The BNBT6-Co and BNBT6-La-Co system have the
  similar curves of e-T and tg d-T.
• The loss tangent is that it almost keeps constant
  through a wide tempera-ture range from the room
  temperature to about 250?

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Results and discussion 5.

• The SEM micrographs of all compositions'
  as-sintered
• surfaces.
• The BNBT6-Co system ? large grain sizes.
• The surface of the grains of Co-doping BNBT6 ? a
  remarkable growth of grains. ( Fig. 3(4) and (6))
• The La 3doping samples without Co3 ? the grain
  size became relatively smaller which was shown in
  BNBT6-La and BNBT6-La-Nb system.
• BNBT6-La -Co system presents a relatively smaller
  grain size than BNBT6-Co system.

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Results and discussion 6.

• The comparison of BNBT6 with BNBT6-La gives a
  similar result ? the sample with La 3 doped has
  a smaller grain size.
• The addition of La ? To restrain the grain growth
  of the ceramics materials
• The addition of Co 3 ? has a converse effect on
  grain size of the ceramics materials.

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Results and discussion 7.

• Table 1 summarizes the dielectric and
  piezoelectric properties of all these modifield
  BNBT6 compositions.
• For all the modified BNBT6 compositions ?
  dielectric constant is greater than that of BNBT6
  at room temperature.
• Piezoelectric coefficient (d33) of BNBT6-La and
  BNBT6-La-Nb, in which La 3 is added, is enhanced
  and the value of mechanical quality factor Qm
  decreases.

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Results and discussion 8.

• The piezoelectric properties of those samples
  doped with Co 3
• ? higher d33 , kt and kp and than other
  compositions.
• BNBT6-Co ? d33 goes up to 139 pC/N ? a maximal
  value of these
• samples. ? the remarkable growth of grain
  size after Co3 -doping
• ? The sound growth of grains makes the
  development of domains more consummate, and thus
  the piezoelectricity of the ceramics is improved.
  
• The grain size of BNBT6-Co ceramics decreases
  after La is added,
• and d33 becomes smaller as well. But BNBT6
  ceramics' dielectric loss
• drops down to 2.3 after Co-doping.
• The Nb5 doping ? the kt/kp ratio of the system
  became bigger ? the
• anisotropy of the ceramics was enhanced.

15
Conclusions

• The piezoelectric properties and the loss tangent
  of BNBT6 system can be improved in some extent by
  Co3 doping.
• The cooperative soft-doping effect of La3 and
  Nb5 could obviously enhance the value of d33 .
• The intermediate phase transition of BNBT6 system
  existing before the Curie temperature almost
  disappears and grain size shows an evident when
  Co3 is doped.