title: Structural and electrical characterisation of some ABO₃ perovskites

authors: Phillips, Roslyn June

abstract: Powder X-ray diffraction and Raman spectroscopy have been used to characterise the electrolyte materials La₁₋ₓSrₓGaO₃₋δ (x = 0-0.2) and LaGa₁₋yMyO₃₋δ (y = 0-0.2, M = Cr, Mg). XRD of La₁₋ₓSrₓGaO₃₋δ (x = 0-0.2) showed the secondary phase of SrGa₃O₇ at >5 mol% Sr. The cell deformed with increasing Sr dopant concentration. In the XRD patterns of LaGa₁₋yCryO₃₋δ (y = 0-0.2) the cell also deformed with increasing Cr dopant concentration. The peak at ca. 32° showed a second peak at 32.37°, likely to be due to a phase change, since the peaks did not alter in relative intensity with increase in dopant concentration (above x = 0). LaGa₁₋yMgyO₃₋δ (y = 0-0.2) showed, from the powder X-ray diffraction pattern, the formation of the secondary phase of La₄Ga₂O₉ at >5 mol% Mg. Raman spectra of LaGaO₃ showed 18 features at room temperature, and 14 at -196 °C with the disappearance of the band at 92 cm⁻¹.  Raman spectra of the doped material, LaGa₁₋yMgyO₃₋δ at y = 0-0.2 showed the formation of a secondary phase of La₄Ga₂O₉ with bands at 243, 295 and 356 cm⁻¹ which become more predominant at 20 mol % Mg.

LaFeO₃ was prepared using a reverse-strike coprecipitation method. The Raman spectrum of LaFeO₃ were obtained at both low-temperature and room temperature, with 9 bands observed of a predicted 24 Raman active modes. Mode assignment was determined from comparison of the Raman profile and band position with perovskites with the same structure, namely, SmAlO₃ and LaGaO₃ and are as follows: 102 (B₁g ), ca.140 (B₂g), 150 (B₁g), 176 (Ag), 227 (B₃g), 261 (Ag), 289 (Ag), 413 (Ag), 429 (B₃g). LaFe₁₋ₓMgₓO₃ was prepared using a reverse-strike coprecipitation method. The XRD patterns obtained at room temperature showed single phase, but also included small amounts of impurity of La₂O₃ and La₂MgOₓ. Lattice calculations based on FeLaO₃ showed that Mg dopant concentration had a minor effect on the overall unit cell volume, with the minimum volume achieved being 241.68Å³ at 1450 °C, 15%Mg concentration. In summary, Mg-doped LaFeO₃ produced a single phase material in the range 0-20 mol% Mg as observed from X-ray diffraction. However, a small amount of impurities in each of the samples was observed, containing La₂O₃ and La₂MgOₓ. The presence of the impurities suggested that an extra calcination step be included in the processing of the material.

LaGdO₃ was fabricated using reverse strike co-precipitation method and sintered at temperature of 1350, 1400 and 1450 °C. X-ray diffraction showed the presence of a single monoclinic phase. Raman spectroscopy showed a spectrum similar for that reported for the B-type rare earth oxide Gd₂O₃ and the band positions of the low temperature Raman spectrum were assigned in comparison with this. A total of 18 bands were identified. Intense broad profile in the region 1000-2000 cm⁻¹ was observed for LaGdO₃, likely due to fluorescent/luminescent bands.

The acceptor-doped perovskite proton conductor SrCe₁₋ₓYₓO₃₋δ (x=0.025 to 0.20, δ = x/2) was prepared and characterised using X-ray diffraction and AC impedance spectroscopy, and the effect of the yttrium dopant concentration on structure and electrical properties has been investigated. X-ray diffraction studies showed a decrease in lattice volume with increasing yttrium content. Electrical conductivity studies were made as a function of oxygen partial pressure, and a partial pressure of water vapour of 0.001 and 0.01 atm. The total conductivity was separated into different components by fitting procedures and regions of ionic and p-type conduction were identified. At 800°C, and at the water vapour partial pressure of 0.01 atm, the ionic conductivity showed a maximum at a doping level of x = 0.10, reaching a value of 5 mS/cm. The conductivity component appearing at low oxygen partial pressure, which according to recent studies may be regarded as protonic rather than n-type, decreased with doping, while the p-type component at high oxygen partial pressure increased.

text: Structural and electrical characterisation of some ABO₃ perovskites Powder X-ray diffraction and Raman spectroscopy have been used to characterise the electrolyte materials La₁₋ₓSrₓGaO₃₋δ (x = 0-0.2) and LaGa₁₋yMyO₃₋δ (y = 0-0.2, M = Cr, Mg). XRD of La₁₋ₓSrₓGaO₃₋δ (x = 0-0.2) showed the secondary phase of SrGa₃O₇ at >5 mol% Sr. The cell deformed with increasing Sr dopant concentration. In the XRD patterns of LaGa₁₋yCryO₃₋δ (y = 0-0.2) the cell also deformed with increasing Cr dopant concentration. The peak at ca. 32° showed a second peak at 32.37°, likely to be due to a phase change, since the peaks did not alter in relative intensity with increase in dopant concentration (above x = 0). LaGa₁₋yMgyO₃₋δ (y = 0-0.2) showed, from the powder X-ray diffraction pattern, the formation of the secondary phase of La₄Ga₂O₉ at >5 mol% Mg. Raman spectra of LaGaO₃ showed 18 features at room temperature, and 14 at -196 °C with the disappearance of the band at 92 cm⁻¹.  Raman spectra of the doped material, LaGa₁₋yMgyO₃₋δ at y = 0-0.2 showed the formation of a secondary phase of La₄Ga₂O₉ with bands at 243, 295 and 356 cm⁻¹ which become more predominant at 20 mol % Mg.

LaFeO₃ was prepared using a reverse-strike coprecipitation method. The Raman spectrum of LaFeO₃ were obtained at both low-temperature and room temperature, with 9 bands observed of a predicted 24 Raman active modes. Mode assignment was determined from comparison of the Raman profile and band position with perovskites with the same structure, namely, SmAlO₃ and LaGaO₃ and are as follows: 102 (B₁g ), ca.140 (B₂g), 150 (B₁g), 176 (Ag), 227 (B₃g), 261 (Ag), 289 (Ag), 413 (Ag), 429 (B₃g). LaFe₁₋ₓMgₓO₃ was prepared using a reverse-strike coprecipitation method. The XRD patterns obtained at room temperature showed single phase, but also included small amounts of impurity of La₂O₃ and La₂MgOₓ. Lattice calculations based on FeLaO₃ showed that Mg dopant concentration had a minor effect on the overall unit cell volume, with the minimum volume achieved being 241.68Å³ at 1450 °C, 15%Mg concentration. In summary, Mg-doped LaFeO₃ produced a single phase material in the range 0-20 mol% Mg as observed from X-ray diffraction. However, a small amount of impurities in each of the samples was observed, containing La₂O₃ and La₂MgOₓ. The presence of the impurities suggested that an extra calcination step be included in the processing of the material.

LaGdO₃ was fabricated using reverse strike co-precipitation method and sintered at temperature of 1350, 1400 and 1450 °C. X-ray diffraction showed the presence of a single monoclinic phase. Raman spectroscopy showed a spectrum similar for that reported for the B-type rare earth oxide Gd₂O₃ and the band positions of the low temperature Raman spectrum were assigned in comparison with this. A total of 18 bands were identified. Intense broad profile in the region 1000-2000 cm⁻¹ was observed for LaGdO₃, likely due to fluorescent/luminescent bands.

The acceptor-doped perovskite proton conductor SrCe₁₋ₓYₓO₃₋δ (x=0.025 to 0.20, δ = x/2) was prepared and characterised using X-ray diffraction and AC impedance spectroscopy, and the effect of the yttrium dopant concentration on structure and electrical properties has been investigated. X-ray diffraction studies showed a decrease in lattice volume with increasing yttrium content. Electrical conductivity studies were made as a function of oxygen partial pressure, and a partial pressure of water vapour of 0.001 and 0.01 atm. The total conductivity was separated into different components by fitting procedures and regions of ionic and p-type conduction were identified. At 800°C, and at the water vapour partial pressure of 0.01 atm, the ionic conductivity showed a maximum at a doping level of x = 0.10, reaching a value of 5 mS/cm. The conductivity component appearing at low oxygen partial pressure, which according to recent studies may be regarded as protonic rather than n-type, decreased with doping, while the p-type component at high oxygen partial pressure increased.

year: 1999

title: Evaluating soil and landscape models to predict liquefaction susceptibility in the Hinuera Formation, Hamilton Basin

authors: McKay, Aleesha

subjects: liquefaction

abstract: Cone Penetration Tests (CPT) derived from the Hamilton section of the Waikato Expressway were analysed within CLiqTM software. The derived Liquefaction Potential Index (LPI) from each CPT was then combined with LIDAR, pedological and geological maps for statistical analysis. A soil model that incorporates the conditions of modern soil development with these derived LPI values was developed as a preliminary assessment tool for liquefaction potential within Hamilton Basin soils. The model shows that liquefaction is more likely to occur on interfluvial areas where there is little topographical relief. Pedological soils with high organic component are also a likely indicator of high liquefaction susceptibility.

text: Evaluating soil and landscape models to predict liquefaction susceptibility in the Hinuera Formation, Hamilton Basin Cone Penetration Tests (CPT) derived from the Hamilton section of the Waikato Expressway were analysed within CLiqTM software. The derived Liquefaction Potential Index (LPI) from each CPT was then combined with LIDAR, pedological and geological maps for statistical analysis. A soil model that incorporates the conditions of modern soil development with these derived LPI values was developed as a preliminary assessment tool for liquefaction potential within Hamilton Basin soils. The model shows that liquefaction is more likely to occur on interfluvial areas where there is little topographical relief. Pedological soils with high organic component are also a likely indicator of high liquefaction susceptibility.

year: 2017

title: Distributed agent-centric system for indigenous data sovereignty

authors: Noovao, Setephano

subjects: holochain

abstract: The sovereignty of indigenous data is a key issue facing indigenous communities. Holochain, a distributed ledger technology, has the potential to address some of the challenges indigenous communities face with respect to data sovereignty. The purpose of this thesis is to critically evaluate the feasibility of using holochain technology to support indigenous data sovereignty. This paper first explores the literature on holochain technology, examining its underlying architecture and features. The research employs a three-phase design science research methodology, conducting an experiment to explore the integration of a decentralized application, holochain, with a prominent cloud service provider. The first phase concentrates on emulating real data-sharing platforms that may utilize data at its disposal, following the principles of indigenous data sovereignty, where a centralized platform could be hosted on a cloud computing service with multiple services in operation. The second phase involves developing a holochain application guided by the principles of indigenous data sovereignty. The final phase seeks to combine the established centralized platform from the first phase with the outcomes of the holochain application from the second phase to experimentally assess whether both technologies can create a data sovereignty solution that aligns with the needs of indigenous data sovereignty. The results of the experiment will provide a solid foundation for understanding the current state of the field and identifying areas where holochain can potentially offer solutions. Furthermore, the results of our research indicate that holochain shows significant promise in tackling the issue of indigenous data sovereignty, although there are considerable limitations that must be addressed and resolved to achieve improved results.

text: Distributed agent-centric system for indigenous data sovereignty The sovereignty of indigenous data is a key issue facing indigenous communities. Holochain, a distributed ledger technology, has the potential to address some of the challenges indigenous communities face with respect to data sovereignty. The purpose of this thesis is to critically evaluate the feasibility of using holochain technology to support indigenous data sovereignty. This paper first explores the literature on holochain technology, examining its underlying architecture and features. The research employs a three-phase design science research methodology, conducting an experiment to explore the integration of a decentralized application, holochain, with a prominent cloud service provider. The first phase concentrates on emulating real data-sharing platforms that may utilize data at its disposal, following the principles of indigenous data sovereignty, where a centralized platform could be hosted on a cloud computing service with multiple services in operation. The second phase involves developing a holochain application guided by the principles of indigenous data sovereignty. The final phase seeks to combine the established centralized platform from the first phase with the outcomes of the holochain application from the second phase to experimentally assess whether both technologies can create a data sovereignty solution that aligns with the needs of indigenous data sovereignty. The results of the experiment will provide a solid foundation for understanding the current state of the field and identifying areas where holochain can potentially offer solutions. Furthermore, the results of our research indicate that holochain shows significant promise in tackling the issue of indigenous data sovereignty, although there are considerable limitations that must be addressed and resolved to achieve improved results.

year: 2024