Structural, magnetic, and transport properties of RxBa1-xTiO3-δ solid solutions, where R = La, Nd, Gd, Er, and Y

Rare-earth-dependent metal-to-semiconductor transitions

Cahit Eylem, Gotthàrd Saghi-Szabó, Bai Hao Chen, Bryan Eichhorn, Jian Liang Peng, Richard Greene, Lourdes Salamanca-Riba, Sahn Nahm

Research output: Contribution to journalArticle

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Abstract

Compositionally homogeneous solid solutions of formula RxBa1-xTiO3-δ (where R = La, Nd; O ≤ x ≤ 1) have been prepared by the dc arc-melting method. The La system showed a negative deviation from Vegard's Law due to BaO deficiencies, whereas the members of the Nd series were stoichiometric and showed a linear relationship between x and the lattice constant a. Limited substitution of the smaller rare earths Gd and Er were also achieved at low values of x (for Gd, 0 ≤ x ≤ 0.4; Er, 0 ≤ x ≤ 0.3) with virtually no substitution at high values of x. Single-phase oxygen deficient cubic YxBa1-xTiO3-δ phases were obtained (where 0 ≤ x ≤ 0.4 and 0 ≤ x ≤ 0.15). Two compositionally dependent phase transitions occur in the La and Nd systems: tetragonal (P4mm)-to-cubic (Pm3m) at very low values of x (<0.05) which is second order and cubic (Pm3m)-to-orthorhombic (Pbnm) at high values of x which appears to be first order. HREM and electron diffraction studies showed no evidence for A-site ordering, microdomain ordering, or superstructure formation in the cubic regions. The single-phase samples disproportionate into BaTiO3 and R2Ti2O7 phases upon heating to 1000°C in air with the exception of La0.33Ba0.67TiO3, which remains cubic upon oxidation with only a 0.8% increase in cell volume. Four-probe resistivity measurements showed metallic conductivities for a majority of the samples between R300 and 4 K with R300 ≈ 10-2-10-4 Ω-cm. Metallic conductivity correlates with the perovskite tolerance factor [t = (rA + r0)/√2(rB + r0)] and occurs when 0.93 < t < 1.02 with semiconducting or insulating behavior occurring outside this range. Dc susceptibility studies showed large Pauli susceptibilities associated with the metallic samples with a correlation between the magnitude of the susceptibility and the number of d electrons. Superconductivity was not observed above 4 K in any of the samples. The effective magnetic moments of the Nd3+ ions in the NdxBa1-xTiO3 phases (ca. 3.3 μB) for x ≤ 0.9 were close to the free ion value (3.62 μB). Electron localization is discussed in terms of structural parameters and electronic effects.

Original languageEnglish
Pages (from-to)1038-1046
Number of pages9
JournalChemistry of Materials
Volume4
Issue number5
Publication statusPublished - 1992 Dec 1
Externally publishedYes

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Transport properties
Rare earths
Structural properties
Solid solutions
Magnetic properties
Substitution reactions
Metals
Ions
Semiconductor materials
Electrons
High resolution electron microscopy
Superconductivity
Magnetic moments
Electron diffraction
Perovskite
Lattice constants
Melting
Phase transitions
Oxygen
Heating

ASJC Scopus subject areas

  • Materials Chemistry
  • Materials Science(all)

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Structural, magnetic, and transport properties of RxBa1-xTiO3-δ solid solutions, where R = La, Nd, Gd, Er, and Y : Rare-earth-dependent metal-to-semiconductor transitions. / Eylem, Cahit; Saghi-Szabó, Gotthàrd; Chen, Bai Hao; Eichhorn, Bryan; Peng, Jian Liang; Greene, Richard; Salamanca-Riba, Lourdes; Nahm, Sahn.

In: Chemistry of Materials, Vol. 4, No. 5, 01.12.1992, p. 1038-1046.

Research output: Contribution to journalArticle

Eylem, Cahit ; Saghi-Szabó, Gotthàrd ; Chen, Bai Hao ; Eichhorn, Bryan ; Peng, Jian Liang ; Greene, Richard ; Salamanca-Riba, Lourdes ; Nahm, Sahn. / Structural, magnetic, and transport properties of RxBa1-xTiO3-δ solid solutions, where R = La, Nd, Gd, Er, and Y : Rare-earth-dependent metal-to-semiconductor transitions. In: Chemistry of Materials. 1992 ; Vol. 4, No. 5. pp. 1038-1046.
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abstract = "Compositionally homogeneous solid solutions of formula RxBa1-xTiO3-δ (where R = La, Nd; O ≤ x ≤ 1) have been prepared by the dc arc-melting method. The La system showed a negative deviation from Vegard's Law due to BaO deficiencies, whereas the members of the Nd series were stoichiometric and showed a linear relationship between x and the lattice constant a. Limited substitution of the smaller rare earths Gd and Er were also achieved at low values of x (for Gd, 0 ≤ x ≤ 0.4; Er, 0 ≤ x ≤ 0.3) with virtually no substitution at high values of x. Single-phase oxygen deficient cubic YxBa1-xTiO3-δ phases were obtained (where 0 ≤ x ≤ 0.4 and 0 ≤ x ≤ 0.15). Two compositionally dependent phase transitions occur in the La and Nd systems: tetragonal (P4mm)-to-cubic (Pm3m) at very low values of x (<0.05) which is second order and cubic (Pm3m)-to-orthorhombic (Pbnm) at high values of x which appears to be first order. HREM and electron diffraction studies showed no evidence for A-site ordering, microdomain ordering, or superstructure formation in the cubic regions. The single-phase samples disproportionate into BaTiO3 and R2Ti2O7 phases upon heating to 1000°C in air with the exception of La0.33Ba0.67TiO3, which remains cubic upon oxidation with only a 0.8{\%} increase in cell volume. Four-probe resistivity measurements showed metallic conductivities for a majority of the samples between R300 and 4 K with R300 ≈ 10-2-10-4 Ω-cm. Metallic conductivity correlates with the perovskite tolerance factor [t = (rA + r0)/√2(rB + r0)] and occurs when 0.93 < t < 1.02 with semiconducting or insulating behavior occurring outside this range. Dc susceptibility studies showed large Pauli susceptibilities associated with the metallic samples with a correlation between the magnitude of the susceptibility and the number of d electrons. Superconductivity was not observed above 4 K in any of the samples. The effective magnetic moments of the Nd3+ ions in the NdxBa1-xTiO3 phases (ca. 3.3 μB) for x ≤ 0.9 were close to the free ion value (3.62 μB). Electron localization is discussed in terms of structural parameters and electronic effects.",
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T1 - Structural, magnetic, and transport properties of RxBa1-xTiO3-δ solid solutions, where R = La, Nd, Gd, Er, and Y

T2 - Rare-earth-dependent metal-to-semiconductor transitions

AU - Eylem, Cahit

AU - Saghi-Szabó, Gotthàrd

AU - Chen, Bai Hao

AU - Eichhorn, Bryan

AU - Peng, Jian Liang

AU - Greene, Richard

AU - Salamanca-Riba, Lourdes

AU - Nahm, Sahn

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N2 - Compositionally homogeneous solid solutions of formula RxBa1-xTiO3-δ (where R = La, Nd; O ≤ x ≤ 1) have been prepared by the dc arc-melting method. The La system showed a negative deviation from Vegard's Law due to BaO deficiencies, whereas the members of the Nd series were stoichiometric and showed a linear relationship between x and the lattice constant a. Limited substitution of the smaller rare earths Gd and Er were also achieved at low values of x (for Gd, 0 ≤ x ≤ 0.4; Er, 0 ≤ x ≤ 0.3) with virtually no substitution at high values of x. Single-phase oxygen deficient cubic YxBa1-xTiO3-δ phases were obtained (where 0 ≤ x ≤ 0.4 and 0 ≤ x ≤ 0.15). Two compositionally dependent phase transitions occur in the La and Nd systems: tetragonal (P4mm)-to-cubic (Pm3m) at very low values of x (<0.05) which is second order and cubic (Pm3m)-to-orthorhombic (Pbnm) at high values of x which appears to be first order. HREM and electron diffraction studies showed no evidence for A-site ordering, microdomain ordering, or superstructure formation in the cubic regions. The single-phase samples disproportionate into BaTiO3 and R2Ti2O7 phases upon heating to 1000°C in air with the exception of La0.33Ba0.67TiO3, which remains cubic upon oxidation with only a 0.8% increase in cell volume. Four-probe resistivity measurements showed metallic conductivities for a majority of the samples between R300 and 4 K with R300 ≈ 10-2-10-4 Ω-cm. Metallic conductivity correlates with the perovskite tolerance factor [t = (rA + r0)/√2(rB + r0)] and occurs when 0.93 < t < 1.02 with semiconducting or insulating behavior occurring outside this range. Dc susceptibility studies showed large Pauli susceptibilities associated with the metallic samples with a correlation between the magnitude of the susceptibility and the number of d electrons. Superconductivity was not observed above 4 K in any of the samples. The effective magnetic moments of the Nd3+ ions in the NdxBa1-xTiO3 phases (ca. 3.3 μB) for x ≤ 0.9 were close to the free ion value (3.62 μB). Electron localization is discussed in terms of structural parameters and electronic effects.

AB - Compositionally homogeneous solid solutions of formula RxBa1-xTiO3-δ (where R = La, Nd; O ≤ x ≤ 1) have been prepared by the dc arc-melting method. The La system showed a negative deviation from Vegard's Law due to BaO deficiencies, whereas the members of the Nd series were stoichiometric and showed a linear relationship between x and the lattice constant a. Limited substitution of the smaller rare earths Gd and Er were also achieved at low values of x (for Gd, 0 ≤ x ≤ 0.4; Er, 0 ≤ x ≤ 0.3) with virtually no substitution at high values of x. Single-phase oxygen deficient cubic YxBa1-xTiO3-δ phases were obtained (where 0 ≤ x ≤ 0.4 and 0 ≤ x ≤ 0.15). Two compositionally dependent phase transitions occur in the La and Nd systems: tetragonal (P4mm)-to-cubic (Pm3m) at very low values of x (<0.05) which is second order and cubic (Pm3m)-to-orthorhombic (Pbnm) at high values of x which appears to be first order. HREM and electron diffraction studies showed no evidence for A-site ordering, microdomain ordering, or superstructure formation in the cubic regions. The single-phase samples disproportionate into BaTiO3 and R2Ti2O7 phases upon heating to 1000°C in air with the exception of La0.33Ba0.67TiO3, which remains cubic upon oxidation with only a 0.8% increase in cell volume. Four-probe resistivity measurements showed metallic conductivities for a majority of the samples between R300 and 4 K with R300 ≈ 10-2-10-4 Ω-cm. Metallic conductivity correlates with the perovskite tolerance factor [t = (rA + r0)/√2(rB + r0)] and occurs when 0.93 < t < 1.02 with semiconducting or insulating behavior occurring outside this range. Dc susceptibility studies showed large Pauli susceptibilities associated with the metallic samples with a correlation between the magnitude of the susceptibility and the number of d electrons. Superconductivity was not observed above 4 K in any of the samples. The effective magnetic moments of the Nd3+ ions in the NdxBa1-xTiO3 phases (ca. 3.3 μB) for x ≤ 0.9 were close to the free ion value (3.62 μB). Electron localization is discussed in terms of structural parameters and electronic effects.

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