Kinetics of Vacancy Doping in SrTiO3 Studied by in situ Electrical Resistivity

The kinetics of annealing to transform stoichiometric SrTiO₃ insulator into a vacancy-doped semiconductor-superconductor was revisited by in situ electrical resistivity measurements. SrTiO₃ single crystals were grown by Floating Zone Method. Using a homemade apparatus several electrical resistivity as a function of time were measured at different temperatures, which allows one to study the creation of vacancies during annealing under vacuum. The activation energy for the oxygen vacancies formation/charge doping in SrTiO₃ was estimated as 1.4±0.3 eV using solid-state kinetics approach.

Keywords:
strontium titanate; crystal growth; solid-state kinetics

Authorship

Felipe Souza Oliveira ^**e-mail: fso@usp.br

Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810, Lorena, SP, BrasilUniversidade de São PauloBrazilLorena, SP, BrazilEscola de Engenharia de Lorena, Universidade de São Paulo, 12602-810, Lorena, SP, Brasil

https://orcid.org/0000-0002-0244-6052

Ana Carolina Favero

Sergio Tuan Renosto

Mário Sérgio da Luz

Instituto de Ciências Tecnológicas e Exatas, Universidade Federal do Triângulo Mineiro, 38025-180, Uberaba, MG, BrasilUniversidade Federal do Triângulo MineiroBrazilUberaba, MG, BrazilInstituto de Ciências Tecnológicas e Exatas, Universidade Federal do Triângulo Mineiro, 38025-180, Uberaba, MG, Brasil

Carlos Alberto Moreira dos Santos

*e-mail: fso@usp.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Formulas

Figures (5)
Formulas (5)

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Figure 1
a) SrTiO₃ powder inside rubber mold (up) and SrTiO₃ feed rod after compressed and sintered (down). b) Single crystal as seed is connected to the Floating Zone furnace holder (up) and SrTiO₃ feed rood prepared for crystal growth process (down). In the pictures (c) to (f) one can see: c) feed rod (up) and seed (down) before feed rod melting; d) feed rod tip melted at hot zone; e) tip melted joined on the single-crystalline seed; and f) both feed rod and seed are pulling down with crystal growing below the hot zone. In (g) in shown a typical SrTiO₃ single crystal rod after the crystal growth.

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Figure 2
XRD pattern of SrTiO₃ powder synthetized by standard ceramic route.

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Figure 3
XRD of the single crystal surface with: a) [100] preferential orientation and b) [110] preferential orientation. The insets show the analyzed samples.

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Figure 4
a) Evolution of the electrical resistivity of a SrTiO₃ single crystal as a function of time during annealing under vacuum of 10^-5 Torr. In (b) is shown the temperature during the annealing. The Inset displays the acquired data at 850^°C setting the initial time just after the plateau mentioned in the text.

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Figure 5
Equilibrium degree evolution calculated by equation (1) at isothermal temperatures of 650ºC (a) and 850ºC (b) under vacuum of 10^-5 Torr. The initial time was set up at the starting point where the annealing temperature becomes stable, such as observed in Figure 4 (a). The insets show the linear model − ln (1 − α) = kt due to the first-order kinetics for the oxygen removal process. The lines are the fitted models.

(1)

(2)

(3)

(4)

(5)

Figure 1 a) SrTiO₃ powder inside rubber mold (up) and SrTiO₃ feed rod after compressed and sintered (down). b) Single crystal as seed is connected to the Floating Zone furnace holder (up) and SrTiO₃ feed rood prepared for crystal growth process (down). In the pictures (c) to (f) one can see: c) feed rod (up) and seed (down) before feed rod melting; d) feed rod tip melted at hot zone; e) tip melted joined on the single-crystalline seed; and f) both feed rod and seed are pulling down with crystal growing below the hot zone. In (g) in shown a typical SrTiO₃ single crystal rod after the crystal growth.

Figure 2 XRD pattern of SrTiO₃ powder synthetized by standard ceramic route.

Figure 3 XRD of the single crystal surface with: a) [100] preferential orientation and b) [110] preferential orientation. The insets show the analyzed samples.

Figure 4 a) Evolution of the electrical resistivity of a SrTiO₃ single crystal as a function of time during annealing under vacuum of 10^-5 Torr. In (b) is shown the temperature during the annealing. The Inset displays the acquired data at 850^°C setting the initial time just after the plateau mentioned in the text.

Figure 5 Equilibrium degree evolution calculated by equation (1) at isothermal temperatures of 650ºC (a) and 850ºC (b) under vacuum of 10^-5 Torr. The initial time was set up at the starting point where the annealing temperature becomes stable, such as observed in Figure 4 (a). The insets show the linear model − ln (1 − α) = kt due to the first-order kinetics for the oxygen removal process. The lines are the fitted models.

(1)

α = \frac{σ - σ_{0}}{σ_{\infty} - σ_{0}},

(2)

g (α) = kt

(3)

k = A \exp (- \frac{E}{k_{B} T}),

(4)

g (α) = - \ln (1 - α),

(5)

α = 1 - e^{- kt} .

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Kinetics of Vacancy Doping in SrTiO3 Studied by in situ Electrical Resistivity

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[1] *e-mail: fso@usp.br