scholarly journals Is Reduced Strontium Titanate a Semiconductor or a Metal?

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 744
Author(s):  
Christian Rodenbücher ◽  
Christo Guguschev ◽  
Carsten Korte ◽  
Sebastian Bette ◽  
Kristof Szot

In recent decades, the behavior of SrTiO3 upon annealing in reducing conditions has been under intense academic scrutiny. Classically, its conductivity can be described using point defect chemistry and predicting n-type or p-type semiconducting behavior depending on oxygen activity. In contrast, many examples of metallic behavior induced by thermal reduction have recently appeared in the literature, challenging this established understanding. In this study, we aim to resolve this contradiction by demonstrating that an initially insulating, as-received SrTiO3 single crystal can indeed be reduced to a metallic state, and is even stable against room temperature reoxidation. However, once the sample has been oxidized at a high temperature, subsequent reduction can no longer be used to induce metallic behavior, but semiconducting behavior in agreement with the predictions of point defect chemistry is observed. Our results indicate that the dislocation-rich surface layer plays a decisive role and that its local chemical composition can be changed depending on annealing conditions. This reveals that the prediction of the macroscopic electronic properties of SrTiO3 is a highly complex task, and not only the current temperature and oxygen activity but also the redox history play an important role.

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Zhuoyu Chen ◽  
Bai Yang Wang ◽  
Adrian G. Swartz ◽  
Hyeok Yoon ◽  
Yasuyuki Hikita ◽  
...  

AbstractAnomalous metallic behavior, marked by a saturating finite resistivity much lower than the Drude estimate, has been observed in a wide range of two-dimensional superconductors. Utilizing the electrostatically gated LaAlO3/SrTiO3 interface as a versatile platform for superconductor-metal quantum phase transitions, we probe variations in the gate, magnetic field, and temperature to construct a phase diagram crossing from superconductor, anomalous metal, vortex liquid, to the Drude metal state, combining longitudinal and Hall resistivity measurements. We find that the anomalous metal phases induced by gating and magnetic field, although differing in symmetry, are connected in the phase diagram and exhibit similar magnetic field response approaching zero temperature. Namely, within a finite regime of the anomalous metal state, the longitudinal resistivity linearly depends on the field while the Hall resistivity diminishes, indicating an emergent particle-hole symmetry. The universal behavior highlights the uniqueness of the quantum bosonic metallic state, distinct from bosonic insulators and vortex liquids.


2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
J. L. Maldonado-Mejía ◽  
J. D. Quiz-Celestino ◽  
M. E. Botello-Zubiate ◽  
S. A. Palomares-Sánchez ◽  
J. A. Matutes-Aquino

In order to gain further insight into the role of substitution of Ru by Nb on superconductivity, polycrystalline samples of Ru1−xNbxSr2Eu1.4Ce0.6Cu2O10−δ  (0.0 ≤x≤ 1.0) have been synthesized by solid-state reaction method. Substitution of Nb at the Ru site in the system takes place isostructurally in the tetragonal structure (space groupI4/mmm) with full solubility (x= 1.0). Superconductivity exists for all compositions. Resistivity measurements in function of temperature from 0 to 300 K were done using the four-probe technique. It is found that the substitution of Ru5+for Nb5+depresses the superconductivity of samples fromTc = 29 K forx= 0.0 toTc = 5 K forx= 1.0 (whereTcis the critical temperature, when resistivity becomes equal to zero). In the normal state, the dependence of resistivity with temperature, for compositions withx = 0.0 and 0.2, shows a metallic behavior, while for compositions betweenx= 0.4 andx= 1 it shows a semiconducting behavior. In that way, the density of charge carriers is reduced with niobium doping, leading to the semiconducting behavior. The resistive transition to the superconducting state of all samples is found to be affected by granularity. Samples undergo double superconducting transition.


2019 ◽  
Author(s):  
Alex Squires ◽  
David Scanlon ◽  
Benjamin Morgan

<p>The Li-stuffed garnets Li<sub><i>x</i></sub>M<sub>2</sub>M<sub>3</sub>′O<sub>12</sub> are promising Li-ion solid electrolytes with potential use in solid-state batteries. One strategy for optimising ionic conductivities in these materials is to tune lithium stoichiometries through aliovalent doping, which is often assumed to produce proportionate numbers of charge compensating Li vacancies. The native defect chemistry of the Li-stuffed garnets, and their response to doping, however, are not well understood, and it is unknown to what degree a simple vacancy-compensation model is valid. Here, we report hybrid density-functional–theory calculations of a broad range of native defects in the prototypical Li-garnet Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub>. We calculate equilibrium defect concentrations as a function of synthesis conditions, and model the response of these defect populations to extrinsic doping. We predict a rich defect chemistry that includes Li and O vacancies and interstitials, and significant numbers of cation-antisite defects. Under reducing conditions, O vacancies act as colour-centres by trapping electrons. We find that supervalent (donor) doping does not produce charge compensating Li vacancies under all synthesis conditions; under Li-rich / Zr-poor conditions the dominant compensating defects are Li<sub>Zr</sub> antisites, and Li stoichiometries strongly deviate from those predicted by simple “vacancy compensation” models.<br></p>


Calphad ◽  
2011 ◽  
Vol 35 (4) ◽  
pp. 623-626 ◽  
Author(s):  
Masato Kato ◽  
Shinya Nakamichi ◽  
Kentaro Takeuchi ◽  
Takeo Sunaoshi

2014 ◽  
Vol 24 (24) ◽  
pp. 3776-3781 ◽  
Author(s):  
Guangyu Jiang ◽  
Jian He ◽  
Tiejun Zhu ◽  
Chenguang Fu ◽  
Xiaohua Liu ◽  
...  

2016 ◽  
Vol 4 (43) ◽  
pp. 16871-16878 ◽  
Author(s):  
Vincenzo Esposito ◽  
De Wei Ni ◽  
Debora Marani ◽  
Francesca Teocoli ◽  
Karl Tor Sune Thydén ◽  
...  

Fast elemental diffusion at the Gd-doped ceria/Y-stabilized zirconia interface occurs under reducing conditions at low oxygen activity and high temperatures.


1996 ◽  
Vol 10 (27) ◽  
pp. 1365-1377 ◽  
Author(s):  
M. CHANDRA SEKHAR ◽  
B. GOPALA KRISHNA ◽  
M. MAHESH KUMAR ◽  
S.V. SURYANARAYANA

Samples with the nominal composition Bi 2 Sr 2 SmCu 2 O y were prepared by solid state reaction method. From the room temperature X-ray diffraction data, it was found that the sample is similar to the Bi-2212 structure. DC electrical resistivity was done from 80 K to 573 K and the impedance measurements were performed from 80 K to 573 K at different frequencies in the range of 10 kHz to 800 kHz. The sample Bi 2 Sr 2 SmCu 2O y has exhibited semiconducting behavior in the low temperature region (80 K to 343 K), metallic behavior in the temperature range of 343 K to 443 K and again semiconducting behavior above 443 K. The sample has exhibited the phenomenon of variable rangehopping mechanism (VRH). The physical parameters related to VRH such as localization length (a), hopping distance (R) and hopping energy (W) have been evaluated and discussed. The activation energy in the high temperature region (above 300 K) decreases with increasing frequency. Tan δ increases with increase in temperature (303 K-573 K), which is attributed to increased conductivity. The dielectric constant increases with increase in temperature. For a given temperature the value of ε is found to decrease with increase in frequency.


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