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Rapid and direct synthesis of complex perovskite oxides through a highly energetic planetary milling

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ABSTRACT

The search for a new and facile synthetic route that is simple, economical and environmentally safe is one of the most challenging issues related to the synthesis of functional complex oxides. Herein, we report the expeditious synthesis of single-phase perovskite oxides by a high-rate mechanochemical reaction, which is generally difficult through conventional milling methods. With the help of a highly energetic planetary ball mill, lead-free piezoelectric perovskite oxides of (Bi, Na)TiO3, (K, Na)NbO3 and their modified complex compositions were directly synthesized with low contamination. The reaction time necessary to fully convert the micron-sized reactant powder mixture into a single-phase perovskite structure was markedly short at only 30–40 min regardless of the chemical composition. The cumulative kinetic energy required to overtake the activation period necessary for predominant formation of perovskite products was ca. 387 kJ/g for (Bi, Na)TiO3 and ca. 580 kJ/g for (K, Na)NbO3. The mechanochemically derived powders, when sintered, showed piezoelectric performance capabilities comparable to those of powders obtained by conventional solid-state reaction processes. The observed mechanochemical synthetic route may lead to the realization of a rapid, one-step preparation method by which to create other promising functional oxides without time-consuming homogenization and high-temperature calcination powder procedures.

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Variation of the weight loss of the milled powders owing to the release of CO2 as a function of the milling time t under different milling conditions.(a) The stoichiometric Bi2O3-Na2CO3-TiO2 powder mixture. (b) The stoichiometric K2CO3-Na2CO3-Nb2O5 powder mixture. The symbols showing the formation of the perovskite phase with the milling time in Fig. 4 were overlapped with each TGA curve. The arrows indicate the activation periods necessary for the dominant formation of perovskite products under each milling condition. The insets show the reaction yields taken from the perovskite periods (steady conditions) of condition numbers 1, 2 and 3.
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f5: Variation of the weight loss of the milled powders owing to the release of CO2 as a function of the milling time t under different milling conditions.(a) The stoichiometric Bi2O3-Na2CO3-TiO2 powder mixture. (b) The stoichiometric K2CO3-Na2CO3-Nb2O5 powder mixture. The symbols showing the formation of the perovskite phase with the milling time in Fig. 4 were overlapped with each TGA curve. The arrows indicate the activation periods necessary for the dominant formation of perovskite products under each milling condition. The insets show the reaction yields taken from the perovskite periods (steady conditions) of condition numbers 1, 2 and 3.

Mentions: The milling-time-dependent TGA scans provided important information about the mechanochemical reaction of the powder mixtures. Because the evolution of CO2 gas with a loss of weight is always indicative of the occurrence of chemical reactions (1) and (2), we were able to evaluate the degree of the completion of the reactions from the amount of CO2 gas released from the thermal decomposition of the carbonates remaining in the milled powder. The TGA curves (Figs 5 and S5) show a decrease in the weight loss of both powder mixtures with a longer milling time. This trend implies the occurrence of reactions (1) and (2) for the formation of the perovskite BNT and KNN. The overall weight losses of the non-milled Bi2O3-Na2CO3-TiO2 and K2CO3-Na2CO3-Nb2O5 mixtures amounted to ca. 5.09% and ca. 11.58%, respectively, slightly higher than those calculated when assuming complete decomposition of the alkali metal carbonates, i.e., ca. 4.94% for Bi2O3-Na2CO3-TiO2 and ca. 11.35% for K2CO3-Na2CO3-Nb2O5. The small discrepancy between the theoretical and experimental values may have originated from the evaporation of small amounts of H2O adsorbed by the hygroscopic reactants during the preparation processes. Notably, their respective weight losses greatly decreased to ca. 2.07% and ca. 3.07% after 40 min of milling under condition number 2.


Rapid and direct synthesis of complex perovskite oxides through a highly energetic planetary milling
Variation of the weight loss of the milled powders owing to the release of CO2 as a function of the milling time t under different milling conditions.(a) The stoichiometric Bi2O3-Na2CO3-TiO2 powder mixture. (b) The stoichiometric K2CO3-Na2CO3-Nb2O5 powder mixture. The symbols showing the formation of the perovskite phase with the milling time in Fig. 4 were overlapped with each TGA curve. The arrows indicate the activation periods necessary for the dominant formation of perovskite products under each milling condition. The insets show the reaction yields taken from the perovskite periods (steady conditions) of condition numbers 1, 2 and 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384223&req=5

f5: Variation of the weight loss of the milled powders owing to the release of CO2 as a function of the milling time t under different milling conditions.(a) The stoichiometric Bi2O3-Na2CO3-TiO2 powder mixture. (b) The stoichiometric K2CO3-Na2CO3-Nb2O5 powder mixture. The symbols showing the formation of the perovskite phase with the milling time in Fig. 4 were overlapped with each TGA curve. The arrows indicate the activation periods necessary for the dominant formation of perovskite products under each milling condition. The insets show the reaction yields taken from the perovskite periods (steady conditions) of condition numbers 1, 2 and 3.
Mentions: The milling-time-dependent TGA scans provided important information about the mechanochemical reaction of the powder mixtures. Because the evolution of CO2 gas with a loss of weight is always indicative of the occurrence of chemical reactions (1) and (2), we were able to evaluate the degree of the completion of the reactions from the amount of CO2 gas released from the thermal decomposition of the carbonates remaining in the milled powder. The TGA curves (Figs 5 and S5) show a decrease in the weight loss of both powder mixtures with a longer milling time. This trend implies the occurrence of reactions (1) and (2) for the formation of the perovskite BNT and KNN. The overall weight losses of the non-milled Bi2O3-Na2CO3-TiO2 and K2CO3-Na2CO3-Nb2O5 mixtures amounted to ca. 5.09% and ca. 11.58%, respectively, slightly higher than those calculated when assuming complete decomposition of the alkali metal carbonates, i.e., ca. 4.94% for Bi2O3-Na2CO3-TiO2 and ca. 11.35% for K2CO3-Na2CO3-Nb2O5. The small discrepancy between the theoretical and experimental values may have originated from the evaporation of small amounts of H2O adsorbed by the hygroscopic reactants during the preparation processes. Notably, their respective weight losses greatly decreased to ca. 2.07% and ca. 3.07% after 40 min of milling under condition number 2.

View Article: PubMed Central - PubMed

ABSTRACT

The search for a new and facile synthetic route that is simple, economical and environmentally safe is one of the most challenging issues related to the synthesis of functional complex oxides. Herein, we report the expeditious synthesis of single-phase perovskite oxides by a high-rate mechanochemical reaction, which is generally difficult through conventional milling methods. With the help of a highly energetic planetary ball mill, lead-free piezoelectric perovskite oxides of (Bi, Na)TiO3, (K, Na)NbO3 and their modified complex compositions were directly synthesized with low contamination. The reaction time necessary to fully convert the micron-sized reactant powder mixture into a single-phase perovskite structure was markedly short at only 30–40 min regardless of the chemical composition. The cumulative kinetic energy required to overtake the activation period necessary for predominant formation of perovskite products was ca. 387 kJ/g for (Bi, Na)TiO3 and ca. 580 kJ/g for (K, Na)NbO3. The mechanochemically derived powders, when sintered, showed piezoelectric performance capabilities comparable to those of powders obtained by conventional solid-state reaction processes. The observed mechanochemical synthetic route may lead to the realization of a rapid, one-step preparation method by which to create other promising functional oxides without time-consuming homogenization and high-temperature calcination powder procedures.

No MeSH data available.


Related in: MedlinePlus