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Abstract

Contents

1. Ferroelectrics (analytical review)

Ferroelectrics - crystal dielectrics, which posess in a certain range of temperatures the spontaneous polarization, which is changing under the influence of external factors.

The Application of ferroelectrics

In the technical application of ferroelectrics was outlined in several areas, the most important of which are as follows [2]:

  1. the manufacture of small-sized low-frequency capacitors with high specific capacity;
  2. the use of materials with a high non-linearity of polarization for dielectric amplifiers, modulators and other managed devices;
  3. use in computing technology as memory elements;
  4. use of crystals ferroelectrics for modulation and conversion of laser radiation;
  5. the manufacture of piezoelectric and of pyroelectric converters.

2. The technological scheme of synthesis of barium titanate

As a start material in oxalate method of obtaining barium titanate we used: titanium tetrachloride (TiCl4), oxalic acid (H2C2O4), barium chloride (BaCl2), ammonia (NH3), distilled water (H2O) [3]. The technological scheme of synthesis of BaTiO3 by oxalate method is shown in picture 2.1.

The technological scheme of synthesis of barium titanate Animation: format - gif, frame - 6, repeats - 50, the duration - 57 sec.

1,4,7 – reactors of dissolution, 2,5,8 – reactors mixing, 3,6,9 – nutch-filters, 10 – drying cupboard, 11 – - muffle furnace

Picture 2.1 – Тhe technological scheme of synthesis of BaTiO3.

3. Synthesis of barium titanate via oxalate precursor

To find the optimum conditions of synthesis of BaTiO3 the mechanism of thermal decomposition of oxalate precursor was studied.

Study of the mechanism of thermal destruction was carried out by methods of differential-thermal (DTA), thermographic (Tg), and X-ray phase analysis (XRF) [3,4,8].

The results of differential-thermal (DTA) and thermographic (TG) analyses by oxalate precursor BaTiO3 with two heating rates are shown in picture 3.1

The results of DTA and TG analyses

Pictute 3.1 – The results of DTA and TG analyses a) - the heating rate is 5 °C/min, b) 10 °C/min.

According to the results of thermal analysis found that in the process of thermal destruction of oxalate precursor temperatures above 280 °C is formed with an intermediate compound Ba[TiO(C2O4)СО3], which in the interval of temperatures 330 - 460 °C with expands on two parallel mechanisms with the formation of unstable products Ba[ТіО2СО3] and Ba[TiO2C2O4], which fall into (α-ВаСО3 + TiO2) and (BaO + TiOC2O4), respectively.[3]

In IR spectra (pic. 3.2) are observed absorption bands corresponding groups of СО32- and C2O42-.

IR spectra

IR spectra: 1 – coprecipitation BaCO3•TiO2, 2 – synthesized Ba[TiO2C2O4] T=20 °C, 3 – product of thermal destruction Ba[TiO(C2O4)2] при T=400 °C, 4 – product of thermal destruction Ba[TiO(C2O4)2] при T= 610 °C, 5 – BaTiO3.

The scheme of the thermal destruction of oxalate precursor

The proposed scheme of the thermal decomposition (pic. 3.3) describes all of the observed features of the TG and DTA analysis.

The scheme of thermal destruction of oxalate precursor

Picture 3.3 – The scheme of thermal destruction of oxalate precursor.

Conclusion

The oxalate method consists in allocation of solutions of poorly soluble oxalic-acid complexes, containing Ba, Ti, and their subsequent thermal decomposition. Analyzed the literature sources on the oxalate method has the following advantages:

  • more pure material;
  • more precise regulation of the composition;
  • the opportunity to obtain crystals in nanosyze;
  • reducing the temperature of synthesis and sintering.

    • On the basis of the investigated the dependences established the conditions and the synthesis of barium titanate by oxalate method. Synthesis includes the following stages:

    1. preparation of initial solutions;
    2. the deposition of barium titaniloxalate;
    3. filtering suspensions and washed sediment barium titaniloxalate;
    4. drying and calcination paste barium titaniloxalate (thermal decomposition).

    The mechanism of reactions of thermal destruction in oxalate precursor involving chemical, x-ray powder, thermographic, differential-thermal analysis methods. The scheme of reactions of formation of intermediate products, the possibility of low-temperature direction synthesis of perovskite phase.

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