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You searched for subject:(Dion Jacobson phase). Showing records 1 – 2 of 2 total matches.

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The Ohio State University

1. Sharits, Andrew R. Structure-Property Relationships in Noncentrosymmetric Layered Perovskites.

Degree: PhD, Chemistry, 2016, The Ohio State University

This work focuses on understanding the structure property relationships in layered perovskites. Certain properties such as ferroelectricity and luminescence are highly dependent upon the crystal structure and can be affected by structural distortions. This makes understanding the crystal structure imperative as it can be adverse or beneficial to the physical property of interest. Perovskites and layered perovskites are prone to structural distortions. As such it is important to understand the forces that drive distortions and how to control them so advantageous properties can be achieved.Chapter 2 discusses the luminescence of Eu3+ in the family of doubly ordered double perovskites NaREMgWO6 (RE = La, Gd, Y). NaYMgWO6, a new member of the family, was found to crystallize in P21 space group and is isostructural with NaGdMgWO6. Emissions characteristic of Eu3+ ions (5D0 -> 7F4, 3, 2, 1,0) were observed, with the most intense transition being the 5D0 -> 7F2 transition near 615 nm. Substitution of Eu3+ onto a more compressed RE site results in a blue shift of the charge transfer excitation band and an increase in the intensity of 5D0 -> 7F2 transition. These hosts display comparable if not better luminescence than Y2O3:Eu3+, a commonly used commercial standard, demonstrating their promise as red phosphors.Chapter 3 and Chapter 4 focus on understanding octahedral tilting, phase transitions and ferroelectric properties in Ruddlesden Popper (RP) phases. Data mining using the ICSD was performed and showed that RP phases typically crystallize in 4 common tilt systems: I4/mmm (a0a0c0), P42/mnm (a0b-c0), Cmcm (a-a-c0) and Cmc21 (a-a-c+). A sorting chart was created using the perovskite tolerance factor and the difference in ionic radii of the A-site cations. This led to the compounds, Ln2SrSc2O7 (Ln= La, Pr, Nd, Sm, Eu, Gd) and Sr3Zr2O7, which fall on the sorting chart in a location that suggests they should be susceptible to a polar distortion. Using distortion mode Rietveld refinements to analyze x-ray and neutron diffraction data, these compounds were discovered to crystallize in the polar space group, Cmc21. Detailed analysis of the phase transitions and ferroelectric properties were explored in La2SrSc2O7 and Nd2SrSc2O7.Chapter 5 focuses on the crystal structures of the family of Dion-Jacobson (DJ) phases, ALnNb2O7 (A=Cs, Rb; Ln= La, Pr, Nd). X-ray diffraction of the structure showed subtle splitting suggesting a lower symmetry than the parent space group P4/mmm. Neutron diffraction of RbLnNb2O7 showed a doubling of the c-axis whereas in the CsLnNb2O7 this was not observed. Synchrotron diffraction showed peak splitting in ALaNb2O7 that had not been observed in the x-ray data. It was found that the RbLaNb2O7 and CsLaNb2O7 crystallized in the nonpolar Cmca and Cmmm space groups, respectively. RbLnNb2O7 (Ln = Pr, Nd) and CsPrNb2O7 were found to crystallize in the polar space groups Ima2 and Pmc21. The driving force behind the octahedral tilting will be discussed. Advisors/Committee Members: Woodward, Patrick (Advisor).

Subjects/Keywords: Chemistry; layered perovskites; Ruddlesden-Popper phase; Dion-Jacobson phase

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Sharits, A. R. (2016). Structure-Property Relationships in Noncentrosymmetric Layered Perovskites. (Doctoral Dissertation). The Ohio State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735

Chicago Manual of Style (16th Edition):

Sharits, Andrew R. “Structure-Property Relationships in Noncentrosymmetric Layered Perovskites.” 2016. Doctoral Dissertation, The Ohio State University. Accessed October 28, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735.

MLA Handbook (7th Edition):

Sharits, Andrew R. “Structure-Property Relationships in Noncentrosymmetric Layered Perovskites.” 2016. Web. 28 Oct 2020.

Vancouver:

Sharits AR. Structure-Property Relationships in Noncentrosymmetric Layered Perovskites. [Internet] [Doctoral dissertation]. The Ohio State University; 2016. [cited 2020 Oct 28]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735.

Council of Science Editors:

Sharits AR. Structure-Property Relationships in Noncentrosymmetric Layered Perovskites. [Doctoral Dissertation]. The Ohio State University; 2016. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1480524956906735


University of St Andrews

2. Dixon, Charlotte A. L. Crystal structure and phase transitions in various functional perovskites.

Degree: PhD, 2018, University of St Andrews

There has been specific interest over the past decade in the discovery and development of new piezoelectric and ferroelectric materials for the use in functional devices, specifically with the aim of replacing the widespread use of PbZrxTi1−xO3. The work detailed in this thesis focuses on the structural characterisation and thermal behaviour of several perovskites possessing interesting physical characteristics, such as ferroelectricity or magnetism. Structural evolution and phase behaviour is characterised using Rietveld refinement techniques on high resolution powder neutron diffraction data. Additional analytical techniques such as symmetry mode analysis, permittivity measurements and second harmonic generation measurements are also often exploited. The work on the LixNa1−xNbO3 system demonstrated a susceptibility to softening of the T4 octahedral tilt mode up to a composition of at least x = 0.12, indicating that the LNN-X solid solution could yield a number of unique perovskite structures. A rationale for how this T4 mode varies across the composition range is offered. The higher doped composition at a value of x = 0.20, displays even more intriguing structural behaviour with the adoption of not one but two variants of the very rare a+a+c− Glazer tilt system. A detailed bond length/bond angle analysis as a function of temperature is used to rationalise the nature of the octahedral distortion that drives the c > a crossover in the rare earth orthoferrite LaFeO3. Symmetry mode analysis is exploited to assist in the structural comparison to the related compound Bi0.5La0.5FeO3, highlighting the anomalous behaviour it exhibits as a result of magnetoelectric coupling effects. The nature of the paraelectric – ferroelectric transition in the layered perovskitelike Dion Jacobson phase, CsBi0.6La0.4Nb2O7 is identified as a direct “avalanche” type transition, making it an example of a hybrid improper ferroelectric. Ferroelectricity in this case does not occur as a result of traditional second-order Jahn-Teller distortions, but is achieved via a mechanism known as trilinear coupling. Experimental analysis is important in understanding the intricacies of this trilinear coupling mechanism. Symmetry mode analysis of CsBi0.6La0.4Nb2O7 shows that two zone boundary primary order parameters (M2+ and M5−) associated with octahedral tilting condense simultaneously, and couple to a zone centre ferroelectric distortion mode (Γ4−). The similar temperature dependency for the two octahedral tilt modes excludes the presence of an intermediary phase, suggesting that the trilinear coupling in this layered phase is strong. Detailed structural characterisations such as those highlighted in this thesis are of fundamental importance as they can identify new design-led approaches to functional materials.

Subjects/Keywords: Symmetry mode analysis; Neutron powder diffraction; Perovskites; Ferroelectricity; Hybrid-improper ferroelectricity; Lithium sodium niobate; Dion-Jacobson phase; LaFeO3; Impedance spectroscopy; ISODISTORT analysis; QD181.O1D5; Perovskite; Oxides – Analysis

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Dixon, C. A. L. (2018). Crystal structure and phase transitions in various functional perovskites. (Doctoral Dissertation). University of St Andrews. Retrieved from http://hdl.handle.net/10023/16572

Chicago Manual of Style (16th Edition):

Dixon, Charlotte A L. “Crystal structure and phase transitions in various functional perovskites.” 2018. Doctoral Dissertation, University of St Andrews. Accessed October 28, 2020. http://hdl.handle.net/10023/16572.

MLA Handbook (7th Edition):

Dixon, Charlotte A L. “Crystal structure and phase transitions in various functional perovskites.” 2018. Web. 28 Oct 2020.

Vancouver:

Dixon CAL. Crystal structure and phase transitions in various functional perovskites. [Internet] [Doctoral dissertation]. University of St Andrews; 2018. [cited 2020 Oct 28]. Available from: http://hdl.handle.net/10023/16572.

Council of Science Editors:

Dixon CAL. Crystal structure and phase transitions in various functional perovskites. [Doctoral Dissertation]. University of St Andrews; 2018. Available from: http://hdl.handle.net/10023/16572

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