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NANOSYSTEMS: PHYSICS, CHEMISTRY, MATHEMATICS, 2013, 4 (3), P. 352-356
STRUCTURE PECULIARITIES OF NANOCRYSTALLINE SOLID SOLUTIONS IN GdAlO3 - GdFeO3 SYSTEM
E. A. Tugova1'2, V. V. Gusarov1'2
1Ioffe Physical Technical Institute of RAS, Saint Petersburg, Russia 2Saint Petersburg State Institute of Technology, Russia [email protected]; [email protected]
PACS 61.46.-w
Nanoparticles of solid solutions in GdAlO3 — GdFeO3 system have been synthesized. Plots of crystalline sizes for GdAl1-xFexO3 series versus GdFeO3 composition have been constructed. The sizes of solid solution nanoparticles were shown to decrease in comparison to the sizes of nanocrystalline individual compounds. The observed regularities allowed us to assume the formation of nanocrystalline GdAl1-xFexO3 series with core-shell morphology.
Keywords: nanostructures, solid solutions, precipitation technique, non-autonomous phases, core-shell nanoparticles.
1. Introduction
Perovskite-type compounds possess unique electrical, magnetic, thermal properties [1-6]. Thus, the research of perovskite-like compounds and solid solutions based on it formation processes, as well as phase equilibria in systems, composing mentioned phases are of great interest [7-10]. Phase relations in pseudo-binary LnAlO3 — LnFeO3 section have been investigated in single works [11, 12] and basically were made for one LaAlO3 — LaFeO3 system. According to the presented data the solubility limits of LaAlO3 and LaFeO3 at 1200 ° C were set to be 0^ x ^0.40 for the LaFei-xAlxO series and 0^ y ^0.15 for LaFeyAl1-yO3 solid solutions [11]. Kuscer et al indicated the formation of continuous LaFe1-xAlxO3 (0^ x ^1) series at 1300 ° C [12]. Previously, samples were prepared by solid-phase chemical reactions using different starting components: hydroxides and oxides[11, 12].
It is of great interest to synthesize solid solutions based on nanoscaled perovskite-like oxides by "soft" chemistry methods [13-16]. The unusual effects observed during nanocrystalline solid solutions formation were fixed [17-19]. The mentioned effects were attributed to a number of factors, including the increase of component's relative solubility in its nanosized state in comparison with macroparticles, the formation of nanoparticles with core-shell morphology and the decreasing of solid solutions nanoparticles sizes in comparison to those of nanocrystalline individual compounds.
These reasons demonstrate the importance of systematic investigations into the peculiarities of nanocrystalline solid solutions, and as a result, structural research with particular interest in the study of nanocrystallite formation in the GdAlO3 — GdFeO3 system was carried out.
2. Experimental
2.1. Synthesis procedure
GdAl i-xFe^Os (0 ^ x ^ 1) series were prepared by precipitation from aqueous solutions of stoichiometric amounts of 1M Gd(NO3^ 5H2O, Fe(NOs)s-9H2O and Al(NO3)3^9H2O. Aqueous 10 wt.% NH4OH was used as the coagulating medium. To this NH4OH solution aqueous solutions of gadolinium, iron and aluminum nitrates were added in a dropwise manner by adjusting the pH to 8-9. The co-precipitated mixtures were filtered immediately after preparation to remove traces of NO- ions and were then dried at room temperature in air. The initial precipitates were subsequently pressed and calcined in air at 600-1300 ° C for 3 h.
2.2. Characterization of prepared nanocrystals
The purity and crystallization of GdAl1-xFexO3 samples were characterized by powder X-ray diffraction (XRD) using a Shimadzu XRD-7000 with monochromatic CuKa radiation (A= 154.178 pm). a-Al2O3 was used as internal standard. Crystallite sizes of the obtained powders were calculated by the X-ray line broadening technique based on Scherer's formula.
3. Results and discussion
Fig.1 shows the X-ray powder diffraction (XRD) data of the initial mixture corresponding to stoichiometry of GdAlO3, heat treated at 600 — 1300 °C for 3 h in air. The results of X-ray analysis of GdAlO3 formation presented in Fig. 1 demonstrate the amorphous state of the initial mixture remains until 1000 ° C. Crystallization of the GdAlO3 phase is fixed at 1000 °C (Fig. 1). The latter is 300 ° C higher than the temperature at which nanocrystalline GdFeO3 is produced [20]. Thus, the investigation of the formation processes for GdAl1-xFexO3 (0< x <1) solid solutions in GdAlO3 — GdFeO3 system was carried out at 1000-1300 ° C. The ratio of components in GdAlO3 — GdFeO3 system was varied in 20 mol. % increments.
The mean size of coherent scattering regions of GdAlO3 and GdFeO3 individual perovskite-like compounds were approximately 60 nm.
The XRD patterns of initial mixtures corresponding to a stoichiometry of GdAl i_xFexO3 (0 < x < 1) series which were heated at 1100 °C are presented in Fig. 2 as an illustration of the processing stages of target solid solutions research.
Fig. 3. shows the relationship between the mean size of coherent scattering regions and interstitial areas for peak with (111) index determined from X-ray data of the GdAl i_xFexO3 series under 1000, 1100 and 1300 ° C versus GdFeO3 content.
The obtained data showed that the crystallite size of GdAlO3 decreased at concentrations ranging from 0.2< x <0.5 (Fig. 3), with the highest GdFeO3 content giving the smallest values of 30—40 nm. These relationships are in agreement with data for interstitial areas (d/n) for the GdAl1-xFexO3 series, for which the observed deviation of plotted d/n values from linearity were typical for solid solutions. These data can be connected with the formation of GdAl1-xFexO3 nanoparticles with core-shell structure type which is in agreement with previous literature [18-19].
1
i tn.mil iM
20 24 28 32 36 4 0 4 4 48 52 56 60 64 68 72 76
20 C)
Fig. 1. X-Ray diffraction patterns of initial mixtures corresponding to stoi-chiometry of GdAlO3 after sintering in air at °C: 1. 600; 2. 800; 3. 1000; 4. 1100; 5. 1300 °C for 3 h
20 24 28 32 40 44 48 52 S 6 60 64 68 72 76
20 H
Fig. 2. X-Ray diffraction patterns, describing processes of GdAl1-xFexO3 series formation for x: 1) 0; 2) 0.2; 3) 0.4; 4) 0.5; 5) 0.6; 6) 0.8; 7) 1 from initial mixtures heat treated at 1100 °C for 3 h
Fig. 3. a) The mean size of coherent scattering regions (D) and b) d/n for GdAl1-xFexO3 series as a function of GdFeO3 content (x)
4. Conclusion
These results showed that the formation of GdAi1-xFexO3 continuous series in the GdAlO3—GdFeO3 system were observed at 1100-1300 °C. GdAl1-xFexO3 nanoparticies ranging from 30-40 nm size were obviously attributed to the core-shell morphology.
Acknowledgments
This work was financially supported by the Russian Foundation for Basic Research, project No 13-03-00888.
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