RU2580117C1 - Ferroelectric ceramic material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: ferroelectric ceramic material contains oxides Bi₂O₃, Fe₂O₃, and TiO₂, with the following ratio of initial components, wt %: Bi₂O₃ 72.80-73.52, Fe₂O₃ 25.72-25.98, TiO₂ 0.50-1.48.

EFFECT: reduction of values of relative dielectric permeability, tangent of dielectric loss angle, increase of stability of dielectric characteristics.

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Description

The invention relates to ferroelectric ceramic materials based on bismuth ferrite and can be used in capacitive magnetoelectric elements of the heads of recording and reading information.

For these applications, the material in the operating temperature range of 25-200 ° C should have the following properties:

- coexisting ferroelectric and magnetic properties, that is, have Curie temperatures T _c and Néel T _N above 200 ° C;

- not have structural instabilities, phase transitions;

- low values of relative permittivity ε / ε ₀ - less than 120, dielectric loss tangent tanδ - less than 0.5 at room temperature, high dielectric stability: close to zero values (ε _{200 ° C-} ε _{25 ° C} ) / ε _{200 ° C,} (ε -ε _{HF LF)} / ε _nch where ε ₂₀₀ ε _{° C} and _{25 ° C} - dielectric constant at 200 ° C and 25 ° C; ε ε _LF and _HF - low frequency at f = 1 kHz and a high-frequency relative permittivity at f = 1 MHz.

при 25°C, K_p=0.237, d₃₃=90 пКл/Н (ЕР 1794820 B1. H01L 41/187, С04В 35/472, С04В 35/453, С01G 49/00. Дата публикации - 12.06.2013) [1]. Для указанных применений материал обладает высокой диэлектрической проницаемостью. Кроме того, при изготовлении материала используется измельчение в среде 2-пропанола, что усложняет технологию.Known ferroelectric ceramic material based on bismuth ferrite, including oxides of bismuth, iron, lanthanum, lead and titanium. The composition of the material corresponds to the chemical formula Bi ( _xy ) La _y Fe _x Pb _1-x Ti _1-x O ₃ , where x = 0.5-0.8 and y = 0.015-0.035. Material has for best formulations.

at 25 ° C, K _p = 0.237, d ₃₃ = 90 pC / N (EP 1794820 B1. H01L 41/187, С04В 35/472, С04В 35/453, С01G 49/00. Date of publication - 12.06.2013) [ one]. For these applications, the material has a high dielectric constant. In addition, in the manufacture of the material, grinding in 2-propanol medium is used, which complicates the technology.

Known ferroelectric material based on bismuth ferrite, including bismuth and iron oxides. The composition of the material corresponds to the chemical formula BiFeO ₃ . The material has the best formulations for ε / ε ₀ (25 ° C, 10 kHz) of 200, (ε ₂₀₀ -ε _{° C 25 ° C)} / ε _{200 ° C} over 0.5, (ε -ε _{HF LF)} / ε _nch more 0.25 (Mazumder R., Chakravarty D., Bhattacharya Dipten, Sen A. Spark plasma sintering of BiFeO _3. // Materials Research Bulletin. 2009. V. 44. P. 555-559) [2].

For these applications, the material has a high dielectric constant and low stability of dielectric characteristics. In addition, the material is synthesized in a cold plasma discharge, which complicates the technology.

Known ferroelectric material based on bismuth ferrite, including oxides of bismuth, barium, zirconium, titanium and iron. The composition of the material corresponds to the chemical formula 0.85BiFeO ₃ -0.15 Ba (Zr _0.6 Ti _0.4 ) O ₃ . The material has ε / ε ₀ = 90 at 25 ° C, 10 kHz, tanδ less than 0.5 at 25 ° C, 10 kHz, (ε _{200 ° C-} ε _{25 ° C} ) / ε _{200 ° C} more than 0.4, (ε _low - ε _high ) / ε _{low bass} less than 0.01 (Choudhary RNP, Perez K., Bhattacharya P., Katiyar RS Structural and dielectric properties of mechanochemically synthesized BiFeO ₃ -Ba (Zr _0.6 Ti _0.4 ) O ₃ solid solutions. // Materials Chemistry and Physics 2007. V. 105. P. 286-292) [3].

For these applications, the material does not have a sufficiently high temperature stability of the dielectric constant (ε _{200 ° C-} ε _{25 ° C} ) / ε _{200 ° C.} In addition, in the manufacture of the material, mechanical activation is used, which increases energy consumption.

A known ferroelectric material is bismuth ferrite BiFeO ₃ (Carvalho TT, Tavares RV Synthesis and thermodynamic stability of multiferroic BiFeO _3. // Materials Letters. 2008. V. 62. P. 3984-3986. [4]. The material contains about 10% impurity phases, is unstable thermodynamically and begins to decompose slowly at the synthesis temperature.

Ferroelectric ceramic material BiFeO ₃ (Mazumder R., Ghosh S., Mondal P., Bhattacherya D., Dasgupta S., Das N., Sen A., Tyagi AK, Sivakumar M., Takami T., Ikuta H. Particle size dependece of magnetization and phase transition near T _N in multiferroic BiFeO _3. // Journal of Applied Physics. V. 100. P. 033908-1-9. 2006) [5] has ε / ε ₀ (25 ° C, 10 kHz ) at 200 tgδ (25 ° C, 10 kHz) less than 1.2, (ε ₂₀₀ -ε _{° C 25 ° C)} / ε _{200 ° C} over 0,9, (ε -ε _{HF LF)} / ε _nch order of 1, 0.

For these applications, the material has high ε / ε ₀ , tanδ and low temperature stability of dielectric characteristics. In addition, the material is produced by the method of "wet" chemistry in combination with solid-phase synthesis.

Known ferroelectric ceramic material based on bismuth ferrite, including oxides of bismuth, titanium and iron. The composition of the material corresponds to the chemical formula BiFe _1-x Ti _x O ₃ , at x = 0.02 ÷ 0.11. The material is characterized by the values of the residual magnetization of 0.2 ÷ 0.25 emu / g. In (BY 13699 C1. С04В 35/26. Date of publication - 15.06.2009) [6]. The patent description does not provide data on the values and temperature stability of dielectric characteristics.

The closest in technical essence to the claimed invention is a material based on bismuth ferrite, including oxides of bismuth, titanium and iron. The composition of the material corresponds to the chemical formula Bi _y Fe _1-x Ti _x O ₃ , at x = 0.0 ÷ 0.3, y = 1.0 ÷ 1.3 (CN 101671173 A. С04В 35/622, С04В 35/453 Date of publication - September 27, 2009) [7], taken as a prototype of the present invention. In the description of the prototype there is no data on the values and temperature stability of the dielectric characteristics.

The objective of the invention is to reduce ε / ε ₀ at 25 ° C, 10 kHz to values less than 120 and tanδ at 25 ° C, 10 kHz to values less than 0.5, increase the stability of dielectric properties (ε _{200 ° C-} ε _{25 ° C} ) / ε _{200 ° C} of less than 0.1, (ε -ε _{HF LF)} / ε _nch less than 0.1.

The specified technical result is achieved in that the ferroelectric ceramic material containing the oxides Bi ₂ O ₃ , Fe ₂ O ₃ , and TiO ₂ according to the invention contains these oxides in the following ratio of the starting components, in wt.%:

Bi ₂ O ₃ 72.80-73.52 Fe ₂ O ₃ 25.72-25.98 TiO ₂ 0.50-1.48

The composition of the material corresponds to the chemical formula:

Bi _0.97 FeO ₃ + x TiO ₂ , x = 0.5-1.5 wt.%

Radiographically established (Abubakarov A.G., Verbenko I.A., Shilkina L.A., Dudkina S.I., Razumovskaya O.N. Phase formation and non-stoichiometry of bismuth ferrite. // Sb-k Proceedings of the All-Russian Conference on the Physics of Ferroelectrics VKS -20., August 18-22, Krasnoyarsk. 2014. S. 167-168) [8] that bismuth ferrite is characterized by structural non-stoichiometry, which leads to the incorporation of a certain part of bismuth ions into the iron sublattice, impaired stoichiometry and the formation of impurity phases . The suppression of this negative phenomenon is possible both due to the use of a smaller amount of bismuth, and due to the modification by oxides of highly charged metals (TiO ₂ ).

In addition, when Ti ^{4+ is} introduced in the case of its partial incorporation into the crystal lattice, a modification scheme of BiFe _1-x Ti _x O _{3 + x / 2} with an excess of oxygen is implemented. The latter is located in internodes and, being ordered, accumulates on certain crystallographic planes, forming Willis clusters of various types: combinations of different ratios of vacancies and internodes (Rao Ch.N.R., Gopalakrishnan J. .. New directions in solid state chemistry (structure, synthesis, properties, reactivity and design of materials). // Novosibirsk: Nauka. 1990. - 520 p.) [9], coherently fused with the original matrix, which leads to the suppression of secondary recrystallization processes and the formation of a finer-grained Keturah and, consequently, to a decrease in ε / ε ₀ and tgδ (Danziger AY, Razumovskaja ON, Reznichenko LA, Sakhnenko VP Klevtsov AN, Dudkin SI Shilkina L.A., Dergunova N.V., Rybyanets A.N. Multicomponent systems of ferroelectric complex oxides: physics, crystal chemistry, technology. Aspects of the design of ferro-piezoelectric materials. // Rostov-on-Don: Publishing house of the Russian State University. 2001-2002. T. 1, 2. - 800 p.) [10].

Moreover, with the predominant localization of highly charged Ti ⁴⁺ ions at the intergranular boundaries, strong chemical bonds are formed with a high proportion of covalency, which leads to a change in the nature of the interphase boundaries from easily deformed mobile media to the cemented framework, which impedes vibrations of any structural elements, including defects in the polycrystalline system (Sadykov Kh.A., Verbenko I.A., Reznichenko L.A., Shilkina L.A., Dudkina S.I., Abubakarov A.G. Influence of ions of transition 3d metals on the formation of electrophysical properties of polycrystalline materials based on alkali metal niobates. // Izv. RAS, Ser.Fiz. 2013. V. 77. No. 9. P. 1253-1255) [11]. This also inevitably leads to a decrease in ε / ε ₀ , tanδ and an increase in the thermal-frequency stability of these characteristics.

The formation of intergranular layers due to the introduction of Ti ⁴⁺ saturated with strong short covalent bonds makes mass transfer between the grains of the main phase and inclusions of impurities more difficult, preventing the decomposition of bismuth ferrite at high temperatures, which leads to a widening of the range of optimal sintering temperatures of the material and allows obtaining ceramics with lower content of impurity phases.

Table 1 - electrophysical characteristics of the ferroelectric material Bi _0.97 FeO ₃ + xTiO ₂ , x = 0.5-1.5 wt.% Depending on the composition;

Table 2 - comparative electrophysical characteristics of the optimal composition of Bi _0.97 FeO ₃ + xTiO ₂ , x = 1 wt.% Of the claimed material and prototype.

An example of the manufacture of ferroelectric ceramic material based on bismuth ferrite

The material was manufactured using conventional ceramic technology. As starting reagents were used oxides of qualification “analytical grade”. The synthesis was carried out by doubling the mixtures, wt.%: Bi ₂ O ₃ = 73.74, Fe ₂ O ₃ = 25.27, TiO ₂ = 1.00 with intermediate grinding of the synthesized product.

The firing temperature of the material T _synt. 1 = 1063 K, T _synt . ₂ = 1073 K, the duration of isothermal holdings τ ₁ = τ ₂ = 5 hours. Sintering of samples in the form of columns ⌀12 mm, height 15-18 mm was carried out at T _{SP .} = 1143 K with the duration of the isothermal hold τ = 2 h Metallizing -. Applying electrodes made by coating the flat surface of the pre-ground portion to a thickness of 1 mm samples silver-containing paste and its subsequent brazing at a temperature T _vzhig. = 1070 K for 0.5 h.

Electrophysical characteristics: relative permittivity ε / ε _{0 of} non-polarized samples at 25 ° C and 200 ° C and frequencies of 1 kHz ε _low and 1 MHz ε _high , the dielectric loss tangent tgδ was determined in accordance with OST 11.0444-87.

The optimal compositions of the claimed material (table. 1, examples No. 3 - No. 5) indicate that the inventive ferroelectric ceramic material based on bismuth ferrite has lower values of ε / ε ₀ , tanδ and the stability of the relative dielectric constant in the temperature range 25 ° C -200 ° C.

The data given in table. 1, 2, confirm the advantages of the proposed ferroelectric ceramic material in comparison with the prototype material, namely, a decrease in ε / ε ₀ to = 116-119 at 25 ° C, 10 kHz and tgδ = 0.17-0.31 at 25 ° C, 10 kHz , stability of dielectric properties (ε _{200 ° C} -ε _{25 ° C)} / ε = _{200 ° C} 0.03-0.09, (ε -ε _{HF LF)} / ε _lf <0.02-0.05. In the best composition, ε / ε ₀ at 25 ° C, 10 kHz = 115, tgδ at 25 ° C, 10 kHz = 0.17, (ε _{200 ° C} -ε _{25 ° C} ) / ε _{200 ° C} = 0.03, ( ε -ε _{HF LF)} / ε _nch = 0.02.

The effect of decreasing ε / ε ₀ at 25 ° C, 10 kHz, tanδ at 25 ° C, 10 kHz and increasing the stability of dielectric properties is achieved by introducing TiO ₂ and the ratio of the starting components.

The inventive ferroelectric material based on bismuth ferrite is structurally stable in the temperature range 25-200 ° C, it is obtained by conventional ceramic technology without the use of energy-intensive mechanical activation and expensive methods of "wet" chemistry, which simplifies the technology in mass production.

Information sources

1. EP 1794820 B1. H01L 41/187, C04B 35/472, C04B 35/453, C01G 49/00. Date of publication - 06/12/2013.

2. Mazumder R., Chakravarty D., Bhattacharya Dipten, Sen A. Spark plasma sintering of BiFeO ₃ . // Materials Research Bulletin. 2009. V. 44. P. 555-559.

3. Choudhary RNP, Perez K., Bhattacharya P., Katiyar RS Structural and dielectric properties of mechanochemically synthesized BiFeO ₃ -Ba (Zr _0.6 Ti _0.4 ) O ₃ solid solutions. // Materials Chemistry and Physics. 2007. V. 105. P. 286-292.

4. Carvalho TT, Tavares PB Synthesis and thermodynamic stability of multiferroic BiFeO ₃ . // Materials Letters. 2008. V. 62. P. 3984-3986.

5. Mazumder R., Ghosh S., Mondal P., Bhattacherya D., Dasgupta S., Das N., Sen A., Tyagi AK, Sivakumar M., Takami T., Ikuta H. Particle size dependece of magnetization and phase transition near T _N in multiferroic BiFeO ₃ . // Journal of Applied Physics. 2006. V. 100. P. 033908-1-9.

6. BY 13699 C1. C04B 35/26. Date of publication - 06/15/2009.

7. CN 101671173 A. C04B 35/622, C04B 35/453. Date of publication - 09/27/2009 - prototype.

8. Abubakarov A.G., Verbenko I.A., Shilkina L.A., Dudkina S.I., Razumovskaya O.N. Phase formation and non-stoichiometry of bismuth ferrite. // Sat-to the proceedings of the All-Russian Conference on Physics of Ferroelectrics VKS-20. g. August 18-22. Krasnoyarsk. 2014.S. 167-168.

9. Rao Ch.N.R., Gopalakrishnan J. .. New directions in solid state chemistry (structure, synthesis, properties, reactivity and design of materials). // Novosibirsk: Science. 1990 .-- 520 p.

10. Danziger A.Ya., Razumovskaya O.N., Reznichenko L.A., Sakhnenko V.P., Klevtsov A.N., Dudkina S.I., Shilkina L.A., Dergunova N.V., Rybyanets A.N. Multicomponent systems of ferroelectric complex oxides: physics, crystal chemistry, technology. Aspects of the design of ferro-piezoelectric materials. // Rostov-on-Don: Publishing house of the RSU. 2001-2002. T. 1.2. - 800 p.

11. Sadykov H.A., Verbenko I.A., Reznichenko L.A., Shilkina L.A., Dudkina S.I., Abubakarov A.G. The effect of transition 3d metal ions on the formation of the electrophysical properties of polycrystalline materials based on alkali metal niobates. // Izv. RAS. Ser. physical 2013.V. 77. No. 9. S. 1253-1255.

Claims (1)

Ferroelectric ceramic material containing oxides Bi ₂ O ₃ , Fe ₂ O ₃ , and TiO ₂ , characterized in that it contains these oxides in the following ratio of starting components, wt.%:
Bi ₂ O ₃ 72.80-73.52
Fe ₂ O ₃ 25.72-25.98
TiO ₂ 0.50-1.48