Search NASA⌕ Search

SEARCH · Search NASA

Results for “LaCrO3”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LaCrO3 by Materials Project

LaCrO3 is (Cubic) Perovskite structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. La3+ is bonded to twelve equivalent O2- atoms to form LaO12 cuboctahedra that share corners with twelve equivalent LaO12 cuboctahedra, faces with six equivalent LaO12 cuboctahedra, and faces with eight equivalent CrO6 octahedra. All La–O bond lengths are 2.78 Å. Cr3+ is bonded to six equivalent O2- atoms to form CrO6 octahedra that share corners with six equivalent CrO6 octahedra and faces with eight equivalent LaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Cr–O bond lengths are 1.96 Å. O2- is bonded in a distorted linear geometry to four equivalent La3+ and two equivalent Cr3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaCrO3 by Materials Project

LaCrO3 is Orthorhombic Perovskite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.40–2.79 Å. Cr3+ is bonded to six O2- atoms to form corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles are 26°. All Cr–O bond lengths are 2.03 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two equivalent Cr3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent La3+ and two equivalent Cr3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaCrO3 by Materials Project

LaCrO3 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. La3+ is bonded in a 3-coordinate geometry to nine equivalent O2- atoms. There are three shorter (2.39 Å) and six longer (2.80 Å) La–O bond lengths. Cr3+ is bonded to six equivalent O2- atoms to form corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles are 24°. All Cr–O bond lengths are 2.02 Å. O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two equivalent Cr3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Evaluation of Doped-LaCrO3 ceramics for high temperature sensor applications

The main objective of this work was to investigate the applicability of the doped-LaCrO3 system for electrical interconnects and sensor applications at temperatures >800°C. Various A- and B-site doping strategies were investigated, and the effect on their electrical conductivity, Seebeck coefficient, and thermal coefficient of expansion were characterized up to 1500ºC. Solid-state, co-precipitation and sol gel methods were used to synthesize the compositions, and the chemical/thermal stability, microstructural evolution, sintering and grain growth kinetics were investigated for these compositions by XRD, SEM and Rietveld methods. The materials showing the greatest promise were included within thick film thermistor and thermocouple sensor designs that were tested to 1500ºC in various gas environments (various pO2 concentrations).

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2021

Electrical, structural and thermomechanical properties of doped-LaCrO3 ceramics for high temperature electronics and sensing applications.

Many important electrical and sensor applications require stable conductors under working temperatures up to 1500oC various redox environments. Common high temperature conductors such as nitrides and carbides are not stable under oxidizing atmospheres, for this reason low redox behavior materials would be more attractive. In this work, further dopant studies of the LaCrO3 system were completed in order to control the electronic and ionic conductivity, as well as the relative chemical and microstructural stability. Neodymium and Niobium dopants were initially studied to control the p-type, and potentially n-type conductive mechanisms, respectively, but other dopants strategies were also investigated. The electrical conductivity and Seebeck coefficient were characterized up to 1500oC under varying oxygen partial pressures. The phase and microstructural evolution of each material was also investigated for these compositions by XRD and SEM. The materials showing the best electrical and thermomechanical performance were included within thick films sensors and were tested.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2021

Tuning magnetic and optical properties through strain in epitaxial LaCrO 3 thin films

We report on the effect of epitaxial strain on magnetic and optical properties of perovskite LaCrO 3 (LCO) single crystal thin films. Epitaxial LCO thin films are grown by pulsed laser deposition on proper choice of substrates to impose different strain states. A combined experimental and theoretical approach is used to demonstrate the direct correlation between lattice-strain and functional properties. The magnetization results show that the lattice anisotropy plays a critical role in controlling the magnetic behavior of LCO films. The strain induced tetragonality in the film lattice strongly affects the optical transitions and charge transfer gap in LCO. This study opens possibilities to tailor the functional properties of LCO and related materials by strain engineering in epitaxial growth.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Volatile products from the interaction of KCl/g/ with Cr2O3 and LaCrO3 in oxidizing environments

Based on cooled target collection methods and high pressure mass spectrometer sampling, oxidative vaporization rates and emanating volatile products were evaluated for interactions of KCl(g) with Cr2O3 and LaCrO3 in oxidizing environments. It was found that: (1) increased rates of oxidative vaporization upon exposure to the reactants are exhibited by chromia and fresh lanthanum chromite samples, and (2) these increased rates result from the heterogeneous formation of complex molecules such as KCl sub 1,2,3CrO3 and KOH sub 1,2CrO3. No increased rates were observed for lanthanum chromite subjected to prolonged oxidative vaporization.

Kohl, F. J.↗
NASA NTRS1977

Volatile products from the interaction of KCl(g) with Cr2O3 and LaCrO3 in oxidizing environments

Cooled target collection techniques and high pressure mass spectrometric sampling were used to measure the relative rates of oxidative vaporization and to identify the volatile products emanating from samples of chromia and Mg-doped lanthanum chromite. The materials were exposed to partial pressures of KCl with and without H2O in one atmosphere of slowly flowing oxygen at elevated temperatures. Chromia and fresh samples of lanthanum chromite exhibited enhanced rates of oxidative vaporization upon exposure to these reactants. Mass spectrometric identification showed that the enhancements resulted from the heterogeneous formation of complex molecules of the type KCl sub 1,2,3 CrO3 and KOH sub l,2 CrO3. Lanthanum chromite that had undergone prolonged oxidative vaporization exhibited no enhanced oxidation upon exposure to the reactants.

Kohl, F. J.↗
DOE OSTI2024

Embedded High-Temperature Sensors: Enhancing Thermoelectrical Performance with Refractory Composites Gradient Layers

To monitor the stability of various energy and manufacturing systems, sensors capable of operating at temperatures exceeding 1000 °C in diverse environments for extended durations are essential. However, under harsh conditions, degradation of sensing materials is a concern that can be controlled by embedding the sensors into refractory oxides. Doped-LaCrO3 based composites are excellent candidates for high-temperature sensing applications due to their good thermoelectrical properties. However, chemical reactivity between the conductive phase and the refractory oxides can decrease the performance of the sensors. In this work, it was devised gradient-type protective layers safeguarding conductive phases within embedded thermocouples, which were fabricated and characterized by X-Ray Diffraction for phase development analysis, Scanning Electron Microscopy and Energy-dispersive X-ray spectroscopy for microstructure and cationic interdiffusion kinetics, long-term thermoelectric testing was completed up to 1400 °C. The enhanced performance of these novel sensors addresses a critical limitation, rendering them viable for long-term high-temperature applications.

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1992

Mg-perovskite/silicate melt partition coefficients in the CMS system at 2430 C and 226 Kbars

The partitioning of elements among lower mantle phases and silicate melts is of interest in unraveling the early thermal history of the Earth. Because of the technical difficulty in carrying out such measurements, only one direct set of measurements has been reported, and these results as well as interpretations based on them have generated controversy. The first set of direct measurements on a synthetic system in the CaO-MgO-SiO2 (CMS) is reported. An experiment was conducted at Stony Brook, using the USSA-2000 split sphere anvil apparatus. An experiment in the CMS system doped with oxides of Al, Ti, Sc, and Sm and run at a nominal temperature of 2380 C and pressure of 226 kbars is reported. Nominal temperatures were measured with a W 3 percent Re/W 25 percent Re thermocouple. The hot spot temperature, where the liquidus is located, is estimated to be at 2430 C. A 10 mm MgO octahedron was used in concert with 4 mm truncation edge lengths on the WC cubes. The sample was contained in a Re capsule which was inserted into a LaCrO3 furnace. Pressure was calibrated at 2000 C. Run duration was approximately 3 minutes. The charge was mounted in epoxy and analyzed using a CAMECA SX-50 electron microprobe. Standard operating conditions were employed, although counting time for the less abundant elements was increased to improved counting statistics. The melt is unquenchable, and forms a dendritic intergrowth of quench crystals and residual melt. It was analyzed using a 30 micron raster. The structural identity of the Mg-perovskite phase was confirmed using x ray microdiffractometry. The results of the investigation are presented.

Mcfarlane, Elisabeth A.↗
NASA NTRS2007

A Symmetrical, Planar SOFC Design for NASA's High Specific Power Density Requirements

Solid oxide fuel cell (SOFC) systems for aircraft applications require an order of magnitude increase in specific power density (1.0 kW/kg) and long life. While significant research is underway to develop anode supported cells which operate at temperatures in the range of 650-800 C, concerns about Cr-contamination from the metal interconnect may drive the operating temperature down further, to 750 C and lower. Higher temperatures, 900-1000 C, are more favorable for SOFC stacks to achieve specific power densities of 1.0 kW/kg. Since metal interconnects are not practical at these high temperatures and can account for up to 75% of the weight of the stack, NASA is pursuing a design that uses a thin, LaCrO3-based ceramic interconnect that incorporates gas channels into the electrodes. The bi-electrode supported cell (BSC) uses porous YSZ scaffolds, on either side of a 10-20 microns electrolyte. The porous support regions are fabricated with graded porosity using the freeze-tape casting process which can be tailored for fuel and air flow. Removing gas channels from the interconnect simplifies the stack design and allows the ceramic interconnect to be kept thin, on the order of 50 -100 microns. The YSZ electrode scaffolds are infiltrated with active electrode materials following the high temperature sintering step. The NASA-BSC is symmetrical and CTE matched, providing balanced stresses and favorable mechanical properties for vibration and thermal cycling.

Cable, Thomas L.↗
NASA NTRS2009

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications.

Cable, Thomas L.↗
DOE OSTI2024

Exploring the impact of multivalent substitution on high-temperature electrical conductivity in doped lanthanum chromite perovskites: An experimental and ab-initio study

Doped LaCrO 3 perovskites hold promise as robust materials for electrical interconnects and sensor applications in harsh environments. In this work, we investigated the high-temperature behavior of La 1–x Sr x CrO 3 , La 1–x Ca x CrO 3 and La 0.8 Sr 0.2 Cr 1-x Mn x O3 (0.1 ≤ x ≤ 0.4) through a combination of computational modeling and physical characterization up to 1500 °C. Crystalline structural properties were determined and compared with ab-initio calculations, which demonstrated excellent agreement with experimental findings. High-temperature electrical conductivity measurements were performed under different atmospheres. Calcium and strontium/manganese co-doped lanthanum chromites exhibited typical semiconductor exponential trends and conductivity showed proportional correlation with substitutions levels up to 30 %. The DFT modelling was completed up to 1500 °C, including low and high temperature chromite phases and oxygen vacancies insertion. Calculations were correlated with experimental electrical properties. This work expands the understanding of doped lanthanum chromites and paves the way for the development of materials suitable for demanding high-temperature applications.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2025

Doping Effects on Multivalence States, Electronic Structure, and Optical Band Gap in LaCrO 3 under Varied Atmospheres: An Integrated Experimental and Density Functional Theory Study

Doping effects on the valence state, electronic structure, and optical band and the effects on electrical conductivity were studied on the doped lanthanum chromite (LaCrO 3 ) system. The specific compositions studied were La 1–x Ca x CrO 3 (LCCx), La 1–x Sr x CrO 3 (LSCx), and La 0.8 Sr 0.2 Cr 1–x Mn x O 3 (LSCMx) (0.1 ≤ x ≤ 0.4). The powders were synthesized using a modified Pechini sol–gel method, and the ceramic samples were densified using a reactive sintering method resulting in densities >96% theoretical. X-ray photoelectron spectroscopy (XPS) was completed to characterize the defect states and cationic valence compensation as a result of divalent (Ca 2+ or Sr 2+ ) and trivalent (Mn 3+ ) substitutions. XPS was completed for samples tested in oxidizing and reducing atmospheres (up to 1500 °C), which provided insights into the oxidation state transitions induced by the Ca 2+ and Sr 2+ dopants. The work notably demonstrated, for the first time, the oxidation/reduction transitions of Cr 4+ to Cr 3+ in Sr 2+ /Mn 3+ co-doped samples under reducing atmospheres. Reflectance UV–vis spectrophotometry optical band gap measurements were also completed for the same materials; a decrease in the optical band gap (2.81–3.12 eV) was shown with increased substitution, suggesting electronic structure modifications in the LaCrO 3 perovskite. Density functional theory calculations validated experimental trends, predicting a diminishing band gap with a rising dopant concentration. The transition in Cr oxidation states was attributed to the presence of divalent/trivalent cations. These findings contribute some insights into methods to tune the LaCrO 3 electrical properties for various low- and high-temperature applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Doped Lanthanum Chromite-refractory Based Composites Sensors for High Temperature Monitoring in Harsh Environments Systems

In order to test and monitor the operational stability and conditions of various energy, and manufacturing systems and their components, development of accurate sensors capable of operating at temperatures in excess of 1000 °C in various environments for long durations is required. In addition, many of these harsh-environment systems do not permit sensors to be directly inserted, so these sensors need to be embedded into thermal protective materials. In this work were developed high-temperature embedded thermocouples composed of various doped lanthanum chromites-refractory based composites synthesized by a mixed-oxide route and directly embedded into a Al2O3 based refractory. The electrical properties were specifically manipulated by altering the level of percolation of the conductive phase within the refractory constituent. Chemical stability of sensors was determined by phase development analysis by X-ray diffraction and X-ray photoelectron spectroscopy; Seebeck coefficients were determined by thermoelectric voltages measurements at temperature up to 1400 oC.

Perovskite LaCrO3, High-temperature conductivity, ↗
DOE OSTI2023

Smart Refractory Sensors Development for Corrosion and Erosion Monitoring in High Temperature Systems

To optimize the operation and functioning of high temperature systems such as slagging gasifiers, coal boilers and glass/steel melters, it is important to monitor corrosion and erosion of refractory used in such systems. Corrosion test strategies are generally based on continuous gravimetric and chemical reactivity monitoring at operational temperatures (750°-1500°C). Both thermocouples and failure sensors and arrays would be useful to monitor the health of any refractory or coatings in these systems. Many of such type of sensors are installed into the systems through open access ports within the refractory; however, there are some disadvantages of this approach where corrosive/erosive gas and molten materials can penetrate and compromise the system. The current work presents the development and performance demonstration of smart refractory with embedded high temperature sensors such as thermocouples, thermistors, and various spallation/crack monitoring sensors, which may be used within a variety of refractory brick in different high temperature processes and applications. The main feature of this technology is that electroceramic based sensors are embedded into smart refractory without significantly impact to the intrinsic properties of the refractory. This technology circumvents the need to insert an isolated monolithic, stand-alone sensor into the refractory via an access port. This technological approach guarantees the integrity and the chemical stability of the materials used in the sensor fabrication within the harsh environment and does not introduce molten material (such as slag) penetration pathways within the refractory. One interesting and important aspect of this innovation is that these embedded sensors can be used to in situ monitoring processes such as chemical reactions and at the same time give information and a deeper understanding of the corrosion and erosion process of the refractory within the system. As stated above, the objective of our work is to develop high-temperature sensors composed of electroceramic materials that are chemically stable at high temperatures (750°-1500°C) and high pressures (up to 1000 psi) that can be used in monitoring corrosion and erosion process in refractory used in high energy systems. The high-temperature sensors investigated in this work were composed of various oxide composites directly embedded into the refractory oxides. The composites used for this work were synthesized by a mixed-oxide route. Metal oxides were inserted within a matrix material composed of refractory oxides (Al2O3, ZrO2, etc.). The physical and electrical properties were specifically manipulated by altering the level of percolation of the conductive species (metal oxides) within the refractory constituent (refractory oxide). Prior to the development of the high-temperature sensors, the oxides composites developed in this study were sintered up to 1600°C under oxidizing atmosphere in order to investigate densification, microstructural evolution, phase development, and their thermoelectrical performance as a function of the composition. The 4-point DC conductivity measurements were performed between 100°-1500°C. The sensors were fabricated from the composite materials by 3D-printing or screen-printing methods into the refractory brick during the consolidation process. An example of one of these embedded sensors consisted of an electroceramic-based thermocouple fabricated with two separate oxide composite compositions which were patterned to produce a couple within the interior of a refractory matrix. The thermocouple successfully displayed thermoelectric voltage trend (as a function of temperature), and the voltage was 220.0 mV around 1400 °C. Corrosion tests on the refractory embedded sensors were performed. To evaluate corrosion in the refractory brick an in-house glass composition was prepared and pressed into pellets and delivered into a pre-cut cavity in the brick. Corrosion experiments results showed the glass penetrated the brick over a 90 h period, and the penetration of the glass through the brick could be monitored by both an amperometric and voltametric based sensor. With this experiment, it was demonstrated that the embedded sensor could dynamically monitor the corrosion process.

20 FOSSIL-FUELED POWER PLANTS↗