Browsing by Author "Bradley Arnold"

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Effect of high-energy radiation on the electrical and optical characteristics of bioactive glasses
(SPIE, 2024) Aria Tauraso; Krishna S. Machuga; Joel McAdams; Ching Hua Su; Brian Cullum; Tagide deCarvalho; Narasimha S. Prasad; Bradley Arnold; Fow-Sen Choa; Kamdeo D. Mandal; Narsingh Bahadur Singh
Significance: The glassy and crystalline hydroxyapatites that affect the metabolic processes such as tissue growth and healing are affected by the electrical, electrochemical, and optical properties investigated in this study. Aim: The aim of the present study is to determine effects of high-energy radiation and impurities on the electrical and optical properties of hydroxyapatites responsible for tissue growth and tendency of glass forming ability. Approach: The approach of the study involves synthesis using carbonates, oxides, silicates, phosphates, and borates of parent materials using elevated temperature and low-temperature flux process. High-energy radiation effects were studied by exposing hydroxyapatites with 5 μCi Cs137 γ- ray source. Morphology was studied to determine dissolution and glass formation of additives such as titanium, gallium, and selenium. Results: Irradiation of silicate bio glasses showed huge effects on the electrical characteristics, such as dielectric constant (hence polarity) and resistivity of the materials while optical properties showed insignificant changes. Morphological studies showed transition of faceted to nonfaceted structure. Conclusion: Exposure for the bias voltage of 50 to 1000 mV in the range of 100 to 100000 Hz frequency range showed a large decrease in the dielectric constant and increase in resistivity. The IR and Raman spectra for irradiated glasses exposed for 24 h showed a small change. Morphological results showed that substitution of gallium, magnesium, and /or titanium affects the transition to the glass formation. The addition of selenium showed enormous potential to improve the mixing and glass formation without titanium and gallium precipitates in the matrix. © 2024 Society of Photo-Optical Instrumentation Engineers (SP.
Low temperature processing of dielectric perovskites for energy storage
(SPIE, 2016) N.B. Singh; Ben Schreib; Michael Devilbiss; Julian Loiacono; Bradley Arnold; Fow-Sen Choa; K.D. Mandal
Since the report of high dielectric value was published for the calcium copper titanate of the stoichiometry CaCu3Ti4O12 (CCTO), several of its analogs such as Yittrium copper titanate Y2/3Cu3Ti4O12 (YCTO), Pr2/3Cu3Ti4O12 (PCTO) and several other compounds have been studied extensively. Most of these materials have demonstrated very high dielectric constants. However, the roadblock is their low resistivity. To overcome this problem, several approaches have been considered, including doping and substitution. In order to solve this problem, we have synthesized the stoichiometric composition and used low temperature processing to grow grains of La2/3Cu3Ti4O12 (LCTO) stoichiometric compound. LCTO with excess copper oxide was also prepared to determine its effect on the morphology and dielectric constant of the stoichiometric LCTO compound. In spite of the low melting point of copper oxide, we observed that excess copper oxide did not show any faster grain growth. Also, the dielectric constant of LCTO was lower than CCTO and unlike CCTO, LCTO showed significant changes as the function of frequency. The measured resistivity was slightly higher than CCTO. © 2016 SPIE.
Morphological evolution and transition at nanoscale in BSTO ceramic materials
(Taylor and Francis Ltd., 2023) N.B. Singh; Ching Hua Su; Fow-Sen Choa; Bradley Arnold; Brian Cullum; K.D. Mandal
Considerable efforts have been devoted since the past three decades for the development of low cost ferroelectric and clean energy storage multifunctional materials. Modification in design and production of a low cost material with well proven process provides pathway for high energy density dielectric energy storage. We studied fluorine doped a commercially well-established material system barium strontium titanate with two different concentrations of dopants and studied the morphological transition and its effect on properties. It was observed that sample with higher concentration transitioned much faster into glassy state, followed by growth of fibers which turned into a self-arranged bird nest type shape. The sample with lower concentration changed slowly into glassy state and only few fibers were farmed. Dielectric was highly dependent on processing methods and shows variation with crystallinity of material, temperature, and cooling conditions during processing. In the higher concentration range, we observed nano-scale interface breakdown very similar to that of solid-liquid interface breakdown during crystal growth. © 2023 Taylor & Francis Group, LLC.