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18
Физика
DOI: 10.14529/mmph180208
FORMATION OF COMPOUNDS BASED ON BISMUTH FERRITE WITH PARTIAL SUBSTITUTION OF BISMUTH IONS BY LANTHANUM AND PRASEODYMIUM
Yu.A. Lupitskaya, D.A. Kalganov, Yu.O. Afanas'ev
Chelyabinsk State University, Chelyabinsk, Russian Federation E-mail: lupitskaya@gmail.com
Using the solid-phase reaction method we obtained bismuth ferrite based compounds generated by partial substitution of bismuth ions with rare earth metal ions (lanthanum and praseodymium). We used thermogravimetric analysis and X-ray analysis at the temperature range from 297 to 1123 K to study the peculiarities of the processes of phase formation of reaction-products synthesis in the systems which contain oxides of iron, bismuth, lanthanum, and praseodymium; their compositions were also determined. For the final synthesis temperature of 1123 K we determined a homogeneous concentration area, where bismuth ferrite solid solutions with the structure of distorted perovskite exist. We studied the influence of lanthanum and praseodymium oxides on phase composition of bismuth ferrite compounds in the process of isovalent alloying of a part of bismuth ions by lanthanum and praseodymium ions. In the frequency range of 20 Hz - 1 MHz we determined the key parameters, which characterize electrical and magnetic properties of perovskite-like phases. We found that for the considered samples the frequency dependencies of complex magnetic permeability and electrical parameters (real and alleged part of permittivity) are of almost the same type. We showed that for the given frequency range both electrical (complex permittivity) and magnetic (complex magnetic permeability) parameters decrease with the frequency increase.
Keywords: bismuth ferrite; solid solutions; distorted perovskite structure; electrical and magnetic properties.
Introduction
Multiferroic materials are inorganic compounds, which have both ferromagnetic and ferroelectric features. Such compounds can be used to create magnetoelectric materials, which can operate in various fields of microelectronics and microwave technology (e. g. extra-high density storage devices: magnetic memory, logical components, magnetic field sensors [1-3]). Therefore, the synthesis of new multiferroic materials attracts the great interest of researchers.
Bismuth ferrite (BiFeO3) is a well-known multiferroic compound, in which dipole ordering occurs near 1100 K and antiferromagnetic ordering - near 640 K. Hence, it can be used for the room temperature applications [4]. Besides, on the base of bismuth ferrite it is possible to create, using sol-gel processing and solid-state synthesis, solid solutions with the broad homogeneous region by double isovalent alloying of a part of Bi3+ ions by rare earth metal ions (Ln3+), and of the same amount of Fe3+ by Co3+ ions. This modification can increase the possible number of application of such compounds [5]. However, the synthesis of monophase ceramic BiFeO3 in the system Bi2O3-Fe2O3 is hindered by the formation of transitional crystalline phases Bi2Fe4O9 and Bi25FeO39.
So, the intent of our work was to investigate the formation of bismuth ferrite solid solution in systems Bi2O3-La2O3-Fe2O3 and Bi2O3-La2O3-Pr6O11-Fe2O3 under heating in air. We considered the influence of lanthanum and praseodymium oxides on the phase composition of bismuth ferrite compounds in the process of isovalent alloying of a part of Bi3+ ions by La3+ and Pr3+ ions. We aimed to determine main parameters, which characterize magnetic and electrical properties of the obtained compounds.
Lupitskaya Yu.A., Kalganov D.A., Formation of compounds based on bismuth ferrite with partial
Afanas'ev Yu.O. substitution of bismuth ions by lanthanum and praseodymium
Experiments
We synthesized polycrystalline samples of solid solutions Bi1-xLaxFeO3 (x = 0; 0,05; 0,1; 1,0) and Bi09-xLa01PrxFeO3 (x = 0; 0,05; 0,1; 0,7) by solid-phase reaction from chemically pure oxides Bi2O3, Fe2O3, La2O3, and Pr6O11. Oxides of rare earth metals (La2O3 and Pr6O11) were thermally annealed at 1273 K for one hour. Mixtures, prepared according to preset quantities of starting reagents, were mixed and thoroughly ground in the agate mortar for 30 minutes with the addition of ethanol. The obtained alcohol-containing load was pressed under the pressure of 50 MPa to cylinders with the diameter of 8 mm and thickness of 1-4 mm. The cylinders were thermally annealed at 1073 K in air for 3 hours. The synthesis of investigated compounds in air was made in the incinerator at T1 = 650 K (3 hours), T2 = 833 K (3 hours), T3 = 1093 K (3 hours) h T4 = 1123 K (6 hours) until the mass of the samples did not change.
We calculated the content of the obtained reaction products by weighting on the analytic balance of 0,05 mg sensitivity.
Thermogravimetric measurements were done dynamically in air for broad temperature range (2971123 K), using the thermogravimetric analyzer "Derivatograph Q-1000" (Paulic-Erdey system) at the heating rate of 10 degrees in one minute.
After every isothermal exposition we examined the qualitative phase composition of the reaction products by the diffractometer DRON-3, using the standard procedure for polycrystalline powder: monochromatic CuKa1 radiation, diffraction angle 26 from 13° to 80°. The synthesized compounds were identified from the International Center for Diffraction Data database (JCPDS-ICDD).
Complex permittivity was calculated using the values of capacity frequency profile and loss angle (alternating current), which were measured in air at room temperature and the frequency range from 20 Hz to 1 MHz. Measurements were done using the meter RLC AKTAKOM AM-3028 (double contact method). Before that we coated the end faces of the cylinders with silver electrodes by baking of a silver conductive paste. We did not take into account errors which stem from the edge electric field and the field irregularities on the electrode surfaces because they are small.
To investigate a frequency profile of complex permeability we used the technique of a solenoid partial filling. We measured the inductance and the Q-factor of the coil with the sample inside. The instrument error was estimated taking into account the coil inductance (without the samples) and losses connected with the coil resistance and eddy currents in it.
Results and discussion
Solid solutions of BiFeO3-LnFeO3 are broadly investigated binary systems, where phases of BiFeO3 and LnFeO3 crystallize in the rhombohedral structure and the orthorhombic structure of perovskite type, respectively [5]. Isovalent alloying of a part of Bi ions by La3+ and Pr3+ ions leads to the formation of solid solution Bi09.xLa01PrxFeO3, in which there is an orthorhombic distortion of perovskite unit cell. The unit cell parameters are determined for the BiFeO3 phase (a = 3,959 A and a = 89°46').
From the analysis of X-ray patterns of Bi1-xLaxFeO3 samples, synthesized by solid-phase reaction, the authors [5] noted that the quantitative content of mullite (Bi2Fe4O9) and sillenite (Bi25FeO39) phases increased with the increase of concentration x, starting from the molecular ratio x > 0.1. This indicates the thermal instability of solid solutions based on bismuth ferrite. However, by X-ray diffraction analysis we showed that solid solutions Bi1-xLaxFeO3 (x = 0; 0,05; 0,1; 1,0) and Bi09-xLa01PrxFeO3 (x = 0; 0,05; 0,1; 0,7) had the crystal structure of perovskite with an orthorhombic distortion (see Fig. 1). Moreover, the percentage of impurity phases Bi2Fe4O9 and Bi25FeO39 did not exceed 3 % at all investigated concentrations x.
Using thermogravimetric analysis we showed that the formation of bismuth ferrite and its derivatives was accompanied by a multistage decrease of samples masses in the broad temperature range (297 - 1123 K), which indicates that physical and chemical processes in the considered systems were staged (see Fig. 2). The differential thermogram (DT) of the base mix [Bi2O3-La2O3-Fe2O3]nH2O had several peaks in low-temperature (520-710 K) and high-temperature regions (780-1123 K), which could be the evidence of change in the oxidation state of the metals in forming compounds (Fig. 2, b).
Вестник ЮУрГУ. Серия «Математика. Механика. Физика» 2018, том 10, № 2, С. 74-79
400 350 300 250
H 200 H
150 100 50 0
a
,........J Л,__________......A...... t.........ft - i. 1 A. в
Lwji—JL^JL,-. -- г
20
30
40
50
60
70
80
20, град.
Fig. 1. X-ray patterns of samples, obtained using solid-phase reaction (T = 1123 K): a - BiFeOs; b - Bio sLao^FeOs; c -BiosLaoiProiFeOs; d - LaFeOs. All samples have the crystal structure of perovskite with an orthorhombic distortion
Am/m ,
H
oth. ед. 0.00
-0.05
-0.10
-0.15
-0.20
-0.25
400
1000
dm/dT, oth.ед.
0 -1 -2 -3 -4 -5 -6 -7
600 800
T, K
Fig. 2. Thermogram (a) and differential thermogram (b) of the base mix [Bi2O3-La2O3-Fe2O3] nH2O
Low-temperature processing of compounds (at 650 K) did not change the phase composition of samples. It can be seen from the XRD patterns with reflexes of the initial reagents of the corresponding oxide systems (see Fig. 3, a). The rise of temperature up to 833 K contributed toward the formation of crystalline phases in the synthesized powders, which can be seen from the appearance of fuzzy diffraction peaks (see Fig. 3, b). These peaks correspond to the reflexes of BiFeO3 phase. Further increase of fusion temperature (in the range 833-1093 K) resulted in the recrystallization process and formation of additional small peaks, which correspond to phases of Bi2Fe4O9 and Bi25FeO39 (Fig. 3, c).
So, by the experimental thermogravimetric and qualitative X-ray diffraction analysis we showed that the formation of bismuth ferrite and its derivatives starts at temperature ~ 833 K, and at T > 833 K BiFeO3 decomposes with the formation of impurity phases. The number of these impurity phases did not rise with the increase of degree of substitution of lanthanum and praseodymium in the synthesized compounds.
Complex permittivity measurements showed that the real part of permittivity S (Fig. 4) and dielectric losses s" (Fig. 5) decreased with the frequency increase. The maximum value of permittivity (S ~ 3750) and the minimum value of dielectric losses (s" ~ 1148) were obtained in the compound Bi0,7La0,iPr0,2FeO3 at frequency f = 1 kHz.
Complex permeability of the considered samples had the similar type of the dependence on frequency as electric parameters (the real and the imaginary parts of permittivity). In the frequency range 20 Hz - 1 MHz the real part of permeability J decreased with the frequency increase. The maximum value of J (~ 496) was obtained in the compound Bi0 9La01FeO3.
Lupitskaya Yu.A., Kalganov D.A., Afanas'ev Yu.O.
Formation of compounds based on bismuth ferrite with partial substitution of bismuth ions by lanthanum and praseodymium
Fig. 3. X-ray patterns of samples, which form in systems BiFeO3 - LaFeO3 and Bi(Pr)FeO3 - LaFeO3 at different fusion temperatures: 650 K (a; 1 - Bi2O3; 2 - La2O3; 3 - Fe2O3), 833 K (b; BiFeO3), 1093 K (c; 1 - BiFeO3; 2 - Bi2Fe4Os; 3 -
Bi25FeO3s)
Fig. 4. Dependence of the real part of permittivity S on the frequency in the range 20 Hz - 1 MHz for compounds: a - Bio,7Lao,1Pro,2FeO3; b - Bio,8Lao,2FeO3; c - Bio,9Lao,1FeO3; d - Bio,8Lao,1Pro,1FeO3
1500
1000
f, кГц
Fig. 5. Dependence of the imaginary part of permittivity £' on the frequency in the range 20 Hz - 1 MHz for compounds: а - Bio,7Lao,iPro,2FeO3; b - Bio,sLao,2FeO3; c - Bio,sLao,iFeO3; d - Bio,sLao,iPro,iFeO3
Вестник ЮУрГУ. Серия «Математика. Механика. Физика» 2oi8, том io, № 2, С. 74-79
f,Kru
Fig. 6. Dependence of the real ji' (a) and the imaginary ji" (b) parts of permeability on the frequency in the range 20 Hz - 1 MHz for the compound Bio,sLao,iFeO3
Conclusion
We determined homogeneous concentration region, where solid solutions Bi1-xLaxFeO3 and Bi09-xLa01PrxFeO3 with the crystal structure of perovskite with an orthorhombic distortion exists. We found that the formation of bismuth ferrite and its derivatives starts at temperature ~ 833 K, and at T > 833 K BiFeO3 decomposes with the formation of impurity phases of mullite (Bi2Fe4O9) and sillenite (Bi25FeO39). The number of these impurity phases does not rise with the increase of degree of substitution of lanthanum and praseodymium in the base compound BiFeO3. We showed that in perovskite-like phases in the frequency range 20 Hz - 1 MHz both electrical (complex permittivity) and magnetic (complex permeability) parameters decrease with the frequency increase. The maximum values of permittivity and permeability / were obtained in the compounds Bi07La01Pr02FeO3 and Bi09La01FeO3, respectively.
Acknowledgments
The reported study was funded by RFBR according to the research project No. 18-33-00269.
References
1. Zvezdin A.K., Pyatakov A.P. Phase transitions and the giant magnetoelectric effect in multiferroics. Phys. Usp. 2004, Vol. 47, no. 4, pp. 416-421. DOI: 10.1070/PU2004v047n04ABEH001752
2. Lupitskaya Y.A., Kalganov D.A., Abdrahmanova K.V. Phase formation in the BaCO3-PbO-Fe2O3-Nb2O5 system. The Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques,, 2017, Vol. 11, no. 1, pp. 87-91. DOI: 10.1134/S1027451016050347
3. Troyanchuk I.O., Bushinsky M.V., Chobot A.N., Mantytskaya O.S., Tereshko N.V. Weak ferro-magnetism in BiFeO3-based multiferroics. Journal of Experimental and Theoretical Physics Letters, 2009, Vol. 89, no. 4, pp. 180-184. DOI: 10.1134/S0021364009040043
4. Troyanchuk I.O., Karpinsky D.V., Bushinsky M.V., Mantytskaya O.S., Tereshko N.V., Shut V.N. Phase Transition, Magnetic and Piezoelectric Properties of Rare-Earth-Substituted BiFeO3 Ceramics. Journal of the American Ceramic Society, 2011, Vol. 94, no. 12, pp. 4502-4506. DOI: 10.1111/j.1551-2916.2011.04780.x
5. Zatyupo A.A., Bashkirov L.A., Petrov G.S., Shichkova T.A. Fiziko-himicheskie svojstva tverdyh rastvorov Bi1-xLaxFe1-xCoxO3, sintezirovannyh s ispol'zovaniem raznyh metodov (Physical and chemical properties of solid solution Bi1-xLaxFe1-xCoxO3 synthesized by different methods. Trudy BGTU. No. 3. Himiya i tekhnologiya neorganicheskih materialov i veshchestv, 2012, no. 3, pp. 37-41. (in Russ.).
Received January 30, 2018
Lupitskaya Yu.A., Kalganov D.A., Afanas'ev Yu.O.
Formation of compounds based on bismuth ferrite with partial substitution of bismuth ions by lanthanum and praseodymium
Bulletin of the South Ural State University Series "Mathematics. Mechanics. Physics" _2018, vol. 10, no. 2, pp. 74-79
УДК 537.9
DOI: 10.14529/mmph180208
ОБРАЗОВАНИЕ СОЕДИНЕНИЙ НА ОСНОВЕ ФЕРРИТА ВИСМУТА ПРИ ЧАСТИЧНОМ ЗАМЕЩЕНИИ ИОНОВ ВИСМУТА ИОНАМИ ЛАНТАНА И ПРАЗЕОДИМА1
Ю.А. Лупицкая, Д.А. Калганов, Ю.О. Афанасьев
Челябинский государственный университет, г. Челябинск, Российская Федерация E-mail: lupitskaya@gmail.com
Методом твердофазной реакции получены соединения на основе феррита висмута, образующиеся при частичном замещении ионов висмута ионами редкоземельных металлов - лантана и празеодима. В интервале температур от 297 до 1123 K методами термогравиметрического и рентгеновского анализа исследованы особенности процессов фазообразования синтеза продуктов реакций в системах, содержащих оксиды железа, висмута, лантана и празеодима, определены их составы. Для конечной температуры синтеза 1123 K выявлена гомогенная концентрационная область существования твердых растворов феррита висмута, имеющих структуру искаженного пе-ровскита. Изучено влияние оксидов лантана и празеодима на фазовый состав соединений феррита висмута при изовалентном легировании части ионов висмута ионами лантана и празеодима. В частотном диапазоне (20 Гц - 1 МГц) установлены основные параметры, характеризующие электрические и магнитные свойства перовскитоподобных фаз. Установлено, что характер частотной зависимости комплексной магнитной проницаемости исследуемых образцов существенно не отличается от частотной зависимости электрических параметров (вещественной и мнимой части диэлектрической проницаемости). Показано, что во всем заданном диапазоне наблюдается уменьшение как электрических (комплексной диэлектрической проницаемости), так и магнитных параметров (комплексной магнитной проницаемости) с ростом частоты.
Ключевые слова: феррит висмута; твердые растворы; структура искаженного перовски-та; электрические и магнитные свойства.
Литература
1. Звездин, А.К. Фазовые переходы и гигантский магнитоэлектрический эффект в мульти-ферроиках / А.К. Звездин, А.П. Пятаков // УФН. - 2004. - Т. 174, № 4. - С. 465-470. DOI: 10.3367/UFNr.0174.200404n.0465
2. Лупицкая, Ю.А. Фазообразование в системе BaCO3-PbO-Fe2O3-Nb2O5 / Ю.А. Лупицкая, Д.А. Калганов, К.В. Абдрахманова // Поверхность. Рентгеновские, синхротронные и нейтронные исследования. - 2016.- № 12. - С. 84-88.
3. Слабый ферромагнетизм в мультиферроиках на основе BiFeO3 / И.О. Троянчук, М.В. Бу-шинский, А Н. Чобот и др. // Письма в ЖЭТФ. - 2009. - Т. 89. - Вып. 4. - С. 204-208.
4. Phase Transition, Magnetic and Piezoelectric Properties of Rare-Earth-Substituted BiFeO3 Ceramics / I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinsky // Journal of the American Ceramic Society. - 2011. - Vol. 94. - Issue 12. - P. 4502-4506.
5. Физико-химические свойства твердых растворов Bii_xLaxFei_xCoxO3, синтезированных с использованием разных методов / А.А. Затюпо, Л.А. Башкиров, Г.С. Петров, Т.А. Шичкова // Труды БГТУ. № 3. Химия и технология неорганических материалов и веществ. - 2012. - № 3. -
С.37-41.
Поступила в редакцию 30 января 2018 г.
1 Исследование выполнено при финансовой поддержке РФФИ в рамках научного проекта № 18-33-00269
Вестник ЮУрГУ. Серия «Математика. Механика. Физика» 2018, том 10, № 2, С. 74-79
