Electronically conductive perovskite-based oxide nanoparticles and films for optical sensing applications
Inventors
Ohodnicki, JR., Paul R. • Schultz, Andrew M.
Assignees
Publication Number
US-9019502-B1
Publication Date
2015-04-28
Expiration Date
2033-12-20
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Abstract
The disclosure relates to a method of detecting a change in a chemical composition by contacting a electronically conducting perovskite-based metal oxide material with a monitored stream, illuminating the electronically conducting perovskite-based metal oxide with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The electronically conducting perovskite-based metal oxide has a perovskite-based crystal structure and an electronic conductivity of at least 10−1 S/cm, where parameters are specified at the gas stream temperature. The electronically conducting perovskite-based metal oxide has an empirical formula AxByO3-δ, where A is at least a first element at the A-site, B is at least a second element at the B-site, and where 0.8<x<1.2, 0.8<y<1.2. Exemplary electronically conducting perovskite-based oxides include but are not limited to La1-xSrxCoO3, La1-xSrxMnO3, LaCrO3, LaNiO3, La1-xSrxMn1-yCryO3, SrFeO3, SrVO3, La-doped SrTiO3, Nb-doped SrTiO3, and SrTiO3-δ.
Core Innovation
The invention provides a method of detecting a change in the chemical composition of a gas stream by utilizing the optical response of an electronically conducting perovskite-based oxide material. This method involves contacting the perovskite-based oxide material with a gas stream, illuminating it with incident light, collecting the exiting light transmitted, reflected, or scattered, monitoring an optical signal based on a comparison of the incident and exiting light using optical spectroscopy, and detecting a shift in this optical signal that indicates a change in chemical composition.
The electronically conducting perovskite-based oxide possesses a perovskite-based crystal structure with an empirical formula AxByO3-δ, high electronic conductivity of at least 10^−1 S/cm at the gas stream temperature, and displays a relatively large and broadband optical absorption from ultraviolet through near-infrared wavelengths. The optical responses of these materials arise from changes in the concentration and mobility of electronic charge carriers and defects that correlate with their high electronic conductivity, which are sensitive to changes in ambient gas atmospheres.
The background presents the problem that existing metal oxide optical gas sensors suffer from limited temperature stability, weak dynamic optical response, poor signal ranges, or require incorporation of noble metals or advanced sensor designs like fiber Bragg gratings that increase cost and complexity. There is a need for sensors operable at high temperatures, providing strong optical signals over broad wavelength ranges without such limitations. This invention addresses these needs by employing electronically conducting perovskite-based oxides with optimized compositions, doping, synthesis, and thermal pretreatment to provide robust, reversible, and monotonic optical signal shifts suitable for harsh environment gas sensing applications.
Claims Coverage
The patent includes 20 claims with multiple inventive features centered on a method for detecting chemical composition changes using electronically conducting perovskite-based oxide materials and related aspects.
Use of electronically conducting perovskite-based oxide material with specified electronic conductivity
The method uses an electronically conducting perovskite-based oxide material exhibiting an electronic conductivity of at least 10^−1 S/cm at the gas stream temperature, having a perovskite-based crystal structure.
Detection of chemical composition changes via shifts in optical signal
The method involves illuminating the oxide material with incident light, collecting exiting light transmitted, reflected, or scattered, monitoring an optical signal based on comparison of incident and exiting light, and detecting shifts in the optical signal to detect chemical composition changes.
Perovskite-based oxide compositional formulation
The electronically conducting perovskite-based oxide has an empirical formula AxByO3-δ, with A-site and B-site elements within specific compositional ranges, including embodiments with doping at A and B sites and control of δ non-stoichiometry.
Operation at elevated temperatures with monotonic optical signal shift
The method monitors gas streams at temperatures at least 200° C., detecting optical signal shifts of at least 0.1% and providing monotonic response to changing concentrations of reducing or oxidizing gases.
Use of barrier layers and waveguide-based interrogation
The method includes embodiments using a barrier layer to separate the gas stream and the monitored stream and employing optical waveguides such as optical fibers with core materials coated by the perovskite-based oxide material for illumination and detection.
Simultaneous electrical and optical monitoring
The method may include measuring electrical resistance of the perovskite-based oxide material concurrently with optical interrogation to enhance sensing capabilities.
Method for determining chemical species concentration
An embodiment provides a method of determining the concentration of a chemical species in the monitored stream using an interrogator device that generates an optical signal measurand proportional to the detected shift and displays a meter reading indicative of the concentration.
Specific method for detecting changes in reducing gas concentration
A method detecting changes in concentration of reducing gases such as H2 in a gas stream at temperatures at least 200° C., using electronically conducting perovskite-based metal oxides with high electronic conductivity (at least 10^2 S/cm) and perovskite structure to monitor shifts in the optical signal.
The claims cover a method that employs electronically conducting perovskite-based oxide materials with specified compositions and electronic conductivity to monitor chemical composition changes in gas streams via shifts in optical signals, including embodiments with advanced interrogation techniques, elevated temperature operation, electrical property measurement, and determination of chemical species concentration.
Stated Advantages
Provides large and broadband optical signal shifts enhancing sensitivity for gas sensing applications.
Operates effectively at elevated temperatures (at least 200°C), overcoming temperature limitations of prior sensors.
Monotonic optical response to varying concentrations allows quantitative chemical species monitoring.
Eliminates the need for costly and complex sensor designs such as fiber Bragg gratings or noble metal incorporation.
Enables combined electrical and optical interrogation, potentially improving selectivity and multi-parameter sensing.
Documented Applications
High temperature gas sensing in harsh environments such as fossil-fueled power plants including oxy-fuel combustion and coal gasification processes.
Monitoring chemical compositions in gas streams for solid oxide fuel cells, combustion turbines, and advanced boiler systems.
Optical sensing of reducing gases (e.g., hydrogen, carbon monoxide, ammonia, hydrocarbons) and oxidizing gases (e.g., oxygen, ozone, NOx, SOx) at elevated temperatures.
Integration with optical fiber based sensors for in situ gas monitoring with potential for temperature and chemical species multi-parameter sensing.
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