Size effect on the crystal structure of barium titanate nanoparticles

Abstract

A size effect on crystal structure has been investigated for barium titanate (BaTiO3) nanoparticles of 40-, 140-, and 430-nm sizes, by means of neutron and high-resolution synchrotron x-ray powder-diffraction and Raman-scattering techniques. These samples were prepared by a modified two-step thermal decomposition method from barium titanyl oxalate, resulting in very few lattice impurities. Rietveld analysis of the neutron-diffraction data for the 430-nm- and 140-nm-sized BaTiO3 particles was performed assuming a single phase of tetragonal (P4mm) structure. The axial ratio c∕a of tetragonal BaTiO3 decreases with a decrease in particle size from 430 to 140 nm. Barium titanate particles with a size of 40 nm consist of (1) tetragonal crystals (83 wt %) with a large cell volume and an axial ratio of unity c∕a=1.000(5) and of (2) a hexagonal phase (P63mmc, 17 wt %) with a large unit-cell volume. Rietveld and maximum-entropy method analyses suggest that there exist atomic displacements from the ideal site of a cubic structure and a spontaneous polarization of the tetragonal phase even in the 40-nm-sized BaTiO3 particles. The nuclear-density distribution of the 140-nm-sized particles with a high dielectric constant does not exhibit a large positional disorder, while the Ba atom of tetragonal BaTiO3 in the 40-nm-sized particles has a smaller atomic displacement parameter.

Size effect of barium titanate: fine particles and ceramics

“…Previous studies reported that the c/a ratio of BaTiO 3 particles decreased with particle size. 1),2),20),21), 28) In contrast, this study revealed that the lattice parameters of the inner tetragonal core were almost consistent with that of BaTiO 3 bulk single crystal. The particle size dependence of c/a ratio should be interpreted as the decrease in the volume fraction of inner tetragonal core.…”

Low temperature synthesis of tetragonal BaTiO3 by using molten salt

“…23) Those for 430 nm size BT fine powder prepared from BaTiO(C 2 O 4 )·4H 2 O were a = 3.99900 (8) and c = 4.03265(9) ¡ (c/a = 1.00842) which were determined by high resolution powder neutron diffraction data. 24) The lattice parameters for BT powder obtained by this work were good agreement with those (a = 3.9940(3) and c = 4.0357(5) ¡ (c/a = 1.0104)) for 500 nm size BT powder prepared by hydrothermal reaction. 8) From the chemical analysis no potassium atom was detected and the Ba/Ti ratio in the tetragonal BaTiO 3 was 1.00.…”

“…4 the endothermic peak in the DTA curve is observed at 130°C for every sample prepared at ²700°C. The T C was somewhat lower than the published value (132°C), 24) and this value agreed well with that for 500 nm size BT powder prepared by hydrothermal reaction. 8) These results suggest that tetragonal BT by this work has similar character to 500 nm size BT powder prepared by hydrothermal reaction.…”

Morphology Control of Metal Oxide Nanocrystals

“…Multilayer ceramic capacitors (MLCC) are indispensable electronic components for advanced electronic technology [2][3][4][5][6][7][8][9][10][11][12] , but larger capacity and smaller size are needed for future electronic devices. To meet these needs, BaTiO 3 particles were downsized, but ferroelectric ceramics lose their ferroelectricity when their particle size is decreased and lose ferroelectricity entirely at a critical size [2][3][4][5][6][7][8][9][10][11] . This is known as the size effect and it impedes the progress of MLCC, so a novel solution has been eagerly anticipated.…”