Emily Yap | University of Wollongong (original) (raw)
Address: Wollongong, Australia
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Over the 100 years of their use, X-ray generators have proven to be indispensable in a wide array... more Over the 100 years of their use, X-ray generators have proven to be indispensable in a wide array of applications. However, the methods for generating X-rays have not developed significantly, and the inherent size and power draw of existing X-ray generators limit the manufacture of more portable X-ray systems. The first demonstration of applying the pyroelectric effect for X-ray generation in 1992 made it a promising candidate for in-field and on-line analyses. This method of thermally cycling a pyroelectric material in a high vacuum exhibits advantages of being lightweight, compact and battery operated.In this thesis, an X-ray generator that utilises the pyroelectric effect was developed and optimised to maximise its performance, in terms of X-ray flux and end-point energy. The generation of X-rays relied on the emission of electrons which was dependent on the electric field created between the pyroelectric crystal and the target placed at a gap distance. Evaluation of the material...
Journal of Applied Physics, 2022
The method of generating x-rays using the pyroelectric effect has garnered interest for applicati... more The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN- xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the pe...
Scripta Materialia, 2018
The lead-free 0.5(Ba 0.7 Ca 0.3)TiO 3 −0.5Ba(Ti 0.8 Zr 0.2)O 3 (BCTZ) ceramics with Er doping hav... more The lead-free 0.5(Ba 0.7 Ca 0.3)TiO 3 −0.5Ba(Ti 0.8 Zr 0.2)O 3 (BCTZ) ceramics with Er doping have shown good upconversion photoluminescence (PL) and desirable optical temperature sensing properties. To bridge a relationship between the structure/intrinsic defects and properties of rare-earth-doped ferroelectrics, we designed and fabricated a series of BCTZ ceramics doped with 1 mol % Er 3+ by combining the firstprinciples calculations and experimental measurements. Theoretically, we discovered that Er can occupy both A sites (i.e., replacing Ba or Ca) and B sites (i.e., replacing Ti or Zr) in the BCTZ lattice and highlighted that the Erdoping-induced vacancy concentration decreases for both the oxygen vacancies (V o) and cation vacancies (V c). Experimentally, the enhanced PL performance and the dielectric, ferroelectric, and piezoelectric properties of the Er-doped BCTZ ceramics have been observed. Finally, the physical origin of Er-induced property enhancement in BCTZ has been elaborated according to the charge density and chemical bonding analysis. These results open up a path to investigate the effects of site substitution and vacancies on optoelectronic properties of multifunctional rare-earthdoped ferroelectrics.
Over the 100 years of their use, X-ray generators have proven to be indispensable in a wide array... more Over the 100 years of their use, X-ray generators have proven to be indispensable in a wide array of applications. However, the methods for generating X-rays have not developed significantly, and the inherent size and power draw of existing X-ray generators limit the manufacture of more portable X-ray systems. The first demonstration of applying the pyroelectric effect for X-ray generation in 1992 made it a promising candidate for in-field and on-line analyses. This method of thermally cycling a pyroelectric material in a high vacuum exhibits advantages of being lightweight, compact and battery operated.In this thesis, an X-ray generator that utilises the pyroelectric effect was developed and optimised to maximise its performance, in terms of X-ray flux and end-point energy. The generation of X-rays relied on the emission of electrons which was dependent on the electric field created between the pyroelectric crystal and the target placed at a gap distance. Evaluation of the material...
Journal of Applied Physics, 2022
The method of generating x-rays using the pyroelectric effect has garnered interest for applicati... more The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN- xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the pe...
Scripta Materialia, 2018
The lead-free 0.5(Ba 0.7 Ca 0.3)TiO 3 −0.5Ba(Ti 0.8 Zr 0.2)O 3 (BCTZ) ceramics with Er doping hav... more The lead-free 0.5(Ba 0.7 Ca 0.3)TiO 3 −0.5Ba(Ti 0.8 Zr 0.2)O 3 (BCTZ) ceramics with Er doping have shown good upconversion photoluminescence (PL) and desirable optical temperature sensing properties. To bridge a relationship between the structure/intrinsic defects and properties of rare-earth-doped ferroelectrics, we designed and fabricated a series of BCTZ ceramics doped with 1 mol % Er 3+ by combining the firstprinciples calculations and experimental measurements. Theoretically, we discovered that Er can occupy both A sites (i.e., replacing Ba or Ca) and B sites (i.e., replacing Ti or Zr) in the BCTZ lattice and highlighted that the Erdoping-induced vacancy concentration decreases for both the oxygen vacancies (V o) and cation vacancies (V c). Experimentally, the enhanced PL performance and the dielectric, ferroelectric, and piezoelectric properties of the Er-doped BCTZ ceramics have been observed. Finally, the physical origin of Er-induced property enhancement in BCTZ has been elaborated according to the charge density and chemical bonding analysis. These results open up a path to investigate the effects of site substitution and vacancies on optoelectronic properties of multifunctional rare-earthdoped ferroelectrics.