Origin of Composition Variation of Ferroelectric Phase Transition Temperature in (Ba,Ca)TiO3 by Synchrotron Radiation Powder Diffraction
The ferroelectric cubic--tetragonal phase transition temperature $T_{\text{C}}$ in (Ba 1-x Ca x )TiO 3 (BCT) is almost unchanged and is maximum at $x \sim 0.06$ in the $T$--$x$ phase diagram, in contrast to many other lead-free BaTiO 3 -based solid solutions that show a decrease in $T_{\text{C}}$ by...
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| Published in | Jpn J Appl Phys Vol. 52; no. 9; pp. 09KF02 - 09KF02-4 |
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| Main Authors | , , , , |
| Format | Journal Article |
| Language | English |
| Published |
The Japan Society of Applied Physics
01.09.2013
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| Online Access | Get full text |
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| Summary: | The ferroelectric cubic--tetragonal phase transition temperature $T_{\text{C}}$ in (Ba 1-x Ca x )TiO 3 (BCT) is almost unchanged and is maximum at $x \sim 0.06$ in the $T$--$x$ phase diagram, in contrast to many other lead-free BaTiO 3 -based solid solutions that show a decrease in $T_{\text{C}}$ by atomic substitution. To investigate the peculiar atomic substitution effect in BCT, the crystal structure parameters and electron density distributions of BCT were analyzed precisely in the cubic phase by synchrotron radiation powder diffraction measurements and the maximum entropy method (MEM)/Rietveld method. The contraction of the lattice induced by the substitution of smaller Ca for Ba promotes the overlap of the electron cloud between the Ti and O atoms in the low $x$ region, whereas it causes the repulsion between the Ti and O atoms in the high $x$ region. The maximum $T_{\text{C}}$ can be attributed to the maximum bonding electron density between the Ti and O atoms at $x \sim 0.06$. |
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| Bibliography: | (Color online) (a) Structure parameters of BCT analyzed in cubic phase (drawn using VESTA). $a$ is a cubic lattice parameter. $U_{\text{Ba/Ca}}$ and $U_{\text{Ti}}$ are isotropic mean-square atomic displacement parameters of the Ba/Ca and Ti atoms, respectively. $U_{\text{O11}}$ and $U_{\text{O22}} = U_{\text{O33}}$ are anisotropic parameters of the O atom, which are parallel and perpendicular to the Ti--O bonds, respectively. (b) Rietveld profile fitting result of BCT ($x = 0.06$) at 415 K. Reliability factors are $R_{\text{WP}} = 0.03118$, $R_{\text{I}} = 0.01265$, and $R_{F} = 0.01706$. The deviation between the observed (+) and calculated (solid line) intensities is drawn at the bottom of the figure with indications of peak positions. The high angular region is enlarged and shown in the insets. (c) and (d) show the $x$ variations of the structure parameters at 415 and 473 K, respectively. (Color online) (a) Electron density distribution of BCT ($x = 0.06$) at 415 K drawn in area of $2a \times 2b \times 2c$. The equi-electron-density surface level is $0.4e$ $Å$ -3 . Contour lines are drawn from $0.4e$ to $1.0e$ $Å$ -3 with $0.1e$ $Å$ -3 intervals. (b) and (c) show the $x$ variations of the minimum electron density $\rho_{\text{min}}$ values between the metal and O atoms at 415 and 473 K, respectively. $\rho_{\text{min}}$(Ti--O) is maximum at $x \sim 0.06$. |
| ISSN: | 0021-4922 1347-4065 |
| DOI: | 10.7567/JJAP.52.09KF02 |