Alotaibi, Meshari ORCID: 0000-0003-1322-6992 (2022) Oxide ion conductivity, Resistive-switching and Ferroelectricity of Doped-HfO2. PhD thesis, University of Sheffield.
Abstract
Yttria-stabilised hafnia, Hf1-xYxO2-x/2 (x=0.15, 0.30 and 0.45), ceramics were prepared by solid state synthesis and characterised by ac impedance spectroscopy. Electrical conductivity of x=0.15 is one order of magnitude higher than x=0.30 and 0.45. All compositions are foremost oxide ion conductors but they contain a small p-type electronic conduction via increasing Y3+ concentration and pO2. YSH materials therefore are mixed conductors. P-type conductivity is attributed to created holes that is believed to be located on under-bonded oxide ions. A study on the effect of a small dc bias on YSH ceramics shows enhancement of their conductivity, transforming into a resistive switching behaviour. This behaviour is novel for any bulk ceramics other than Ca-doped BiFeO3. Switching of YSH depends on both oxygen partial pressure, pO2, and temperature. At low applied voltage, the increase in the conductivity is associated with p-type behaviour commenced at the positive electrode/ceramic interface, but with further applied voltage, YSH underwent a transition from p-type to n-type behaviour which is commenced at the negative electrode/ceramics interface. With increasing applied voltage, the total conductivity enhanced sharply by 1.5- 2.5 orders of magnitude that is reversible with hysteresis under removal of the applied voltage. The ac impedance results of Hf1-xZrxO2 thin films demonstrate a single homogeneous component attributed to the bulk layer. Resistance of all compositions decreased with increasing pO2 (N2-Air-O2). This decrease in resistance is associated with p-type electronic conduction. In p-type materials, a decrease in resistance is related to the increase in number of holes that can probably be located on under-bonded oxygen or created during the preparation of the thin films. The equivalent circuit of a resistor in parallel with a seriesconnected CPE-C element gave best fitting to HZO thin film samples. Results of fixed frequency variable temperature sweeps of permittivity, er, of HZO show a sharp peak at 464- 474 °C with a maximum permittivity of ~ 11100. This result is the first report of a peak in the permittivity of HZO thin films that is attributed to a transition from ferroelectric into paraelectric behaviour at Tc.
Metadata
Supervisors: | West, Anthony R |
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Related URLs: | |
Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield) |
Identification Number/EthosID: | uk.bl.ethos.875046 |
Depositing User: | Mr Meshari Alotaibi |
Date Deposited: | 07 Mar 2023 13:44 |
Last Modified: | 01 Aug 2023 09:53 |
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