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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.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Data and script associated with “Shifts in Rain-Snow Partitioning Drive Faster Water Transit Times in the US Pacific Northwest”

This data package contains the data and code to use and run the Water Tracer enabled version of the Weather Research and Forecasting Hydrologic model (WT-WRF-Hydro) with the Sequential Precipitation Input Tagging (SPIT) framework. It is associated with the publication “Shifts in Rain-Snow Partitioning Drive Faster Water Transit Times in the US Pacific Northwest” published in Scientific Reports (Butler et al., 2026; https://doi.org/10.1038/s41598-026-46539-1). We use the Continental U.S. (CONUSII; Rasmussen et al., 2021) dataset to force the model with an historical climate (2006–2013) and a future climate (2086–2093) with a representative carbon pathway (RCP) 8.5 scenario. We use the model to calculate water transit times in five headwater catchments within the U.S. Pacific Northwest. We also show key hydrologic and environmental variables that affect water transit times and changes in the future. Finally, we use observed data to validate the model such as stream water isotopes, snowpack characteristics, and stream discharge. For details on how to navigate data packages generated by this project, see https://data.ess-dive.lbl.gov/portals/PNNLRiverCorridorSFA/About. In addition to a readme, this data package also includes a file-level metadata (FLMD) file that describes each file and a data dictionary (DD) that describes all column/row headers and variable definitions. The data package consists of 11 folders: (1) "Figures" contains the exported figures used in the manuscript; (2) "Model_Isotope_Date" contains the WT-WRF-Hydro isotope date used in model validation; (3) “Model_Outputs_Future” contains the WT-WRF-Hydro future climate outputs; (4) “Model_Outputs_Historical” contains the WT-WRF-Hydro historical climate outputs; (5) “Model_Outputs_Weights_Areas” contains the WT-WRF-Hydro weights per catchment used to calculate water transit times and isotopes in stream water; (6) “MODIS_data_scripts” contains data used to validate snow conditions in the study area; (7) “Observed_Flow_Data” contains the observed streamflow data used in model validation; (8) “Observed_Isotope_Data” contains the observed stream water isotope data used in model validation; (9) “Scripts” contains the Python scripts used to general results and the figures; (10) “Statistic_Outputs” contains the water transit time statistical outputs reported in this manuscript; (11) “Validation_SNOTEL” contains the SNOTEL data used in model validation. The files in this data package have the following file extensions: .tif, .txt, .csv, .pdf, .py, .jpg, and .png.

American River↗
DOE OSTI2017

Diagnosing phosphorus limitations in natural terrestrial ecosystems in carbon cycle models

Abstract Most of the Earth System Models ( ESMs ) project increases in net primary productivity ( NPP ) and terrestrial carbon (C) storage during the 21st century. Despite empirical evidence that limited availability of phosphorus (P) may limit the response of NPP to increasing atmospheric CO 2 , none of the ESMs used in the previous Intergovernmental Panel on Climate Change assessment accounted for P limitation. We diagnosed from ESM simulations the amount of P need to support increases in carbon uptake by natural ecosystems using two approaches: the demand derived from (1) changes in C stocks and (2) changes in NPP . The C stock‐based additional P demand was estimated to range between −31 and 193 Tg P and between −89 and 262 Tg P for Representative Concentration Pathway ( RCP ) 2.6 and RCP8.5 , respectively, with negative values indicating a P surplus. The NPP ‐based demand, which takes ecosystem P recycling into account, results in a significantly higher P demand of 648–1606 Tg P for RCP2 .6 and 924–2110 Tg P for RCP8 .5. We found that the P demand is sensitive to the turnover of P in decomposing plant material, explaining the large differences between the NPP ‐based demand and C stock‐based demand. The discrepancy between diagnosed P demand and actual P availability (potential P deficit) depends mainly on the assumptions about availability of the different soil P forms. Overall, future P limitation strongly depends on both soil P availability and P recycling on ecosystem scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

What would it take to achieve the Paris temperature targets?

Here, the 2015 Paris Agreement aims to limit warming to 2 or 1.5°C above preindustrial level, although combined Intended Nationally Determined Contributions (INDCs) are likely insufficient to achieve these targets. We propose a set of idealized emission pathways consistent with the targets. If countries reduce emissions in line with their INDCs, the 2°C threshold could be avoided only if net zero greenhouse gas emissions (GHGEs) are achieved by 2085 and late century negative emissions are considerably in excess of those assumed in Representative Concentration Pathway (RCP) 2.6 (net –5 Gt CO 2 /yr, compared with –1.5 Gt CO 2 /yr in RCP2.6). More aggressive near-term reductions would allow 2°C to be avoided with less end-of-century carbon removal capacity. A 10% cut in GHGEs by 2030 (relative to 2015) could likely achieve 2°C with RCP2.6 level negative emissions. The 1.5°C target requires GHGEs to be reduced by almost a third by 2030 and net zero by 2050, while a 50 year overshoot of 1.5°C allows net zero GHGEs by 2060.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Impact of tropical cyclones on modeled extreme wind-wave climate

Here, the effect of forcing wind resolution on the extremes of global wind-wave climate are investigated in numerical simulations. Forcing winds from the Community Atmosphere Model at horizontal resolutions of ~1.0° and ~0.25° are used to drive Wavewatch III. Differences in extreme wave height are found to manifest most strongly in tropical cyclone (TC) regions, emphasizing the need for high-resolution forcing in those areas. Comparison with observations typically show improvement in performance with increased forcing resolution, with a strong influence in the tail of the distribution, although simulated extremes can exceed observations. A simulation for the end of the 21st century under a RCP 8.5 type emission scenario suggests further increases in extreme wave height in TC regions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Observational needs for estimating Alaskan soil carbon stocks under current and future climate

Abstract Representing land surface spatial heterogeneity when designing observation networks is a critical scientific challenge. Here we present a geospatial approach that utilizes the multivariate spatial heterogeneity of soil‐forming factors—namely, climate, topography, land cover types, and surficial geology—to identify observation sites to improve soil organic carbon (SOC) stock estimates across the State of Alaska, USA. Standard deviations in existing SOC samples indicated that 657, 870, and 906 randomly distributed pedons would be required to quantify the average SOC stocks for 0–1 m, 0–2 m, and whole‐profile depths, respectively, at a confidence interval of 5 kg C m −2 . Using the spatial correlation range of existing SOC samples, we identified that 309, 446, and 484 new observation sites are needed to estimate current SOC stocks to 1 m, 2 m, and whole‐profile depths, respectively. We also investigated whether the identified sites might change under future climate by using eight decadal (2020–2099) projections of precipitation, temperature, and length of growing season for three representative concentration pathway (RCP 4.5, 6.0, and 8.5) scenarios of the Intergovernmental Panel on Climate Change. These analyses determined that 12 to 41 additional sites (906 + 12 to 41; depending upon the emission scenarios) would be needed to capture the impact of future climate on Alaskan whole‐profile SOC stocks by 2100. The identified observation sites represent spatially distributed locations across Alaska that captures the multivariate heterogeneity of soil‐forming factors under current and future climatic conditions. This information is needed for designing monitoring networks and benchmarking of Earth system model results.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Magnetocaloric Effect in Lightly‐Doped Fe 5 Si 3 Single Crystals

Abstract Development of promising new materials for above room temperature magnetic cooling applications relies on careful balancing of structure and composition to maximize accessible metastable phases that can drive a strong magnetocaloric effect (MCE). However, the working temperatures of these materials may fall outside of desired application windows. In this work, it is shown that it is possible to control metastable phase stability temperatures of Fe 5 Si 3 through selection of appropriate spin and charge doping. Here, the parent material's desired structure appears only within a narrow temperature range from 1098 to 1303 K. Doping with Mn and P is shown to allow stabilization of the parent's high temperature phase and resulting MCE to room temperature. The structural and magnetic properties, and the magnetocaloric effect of single crystal Fe 4.83 Mn 0.16 Si 2.91 P 0.09 (FMSP) are investigated experimentally and theoretically. A first‐order magneto‐elastic transition is observed at 348 K, where magnetic onset is accompanied by a change in lattice volume without an apparent change in crystal symmetry. Although the trace Mn and P doping are found to decrease the T C , the maximum magnetic entropy change Δ S Max ( T ) and the relative cooling power (RCP) of FMSP are enhanced compared to polycrystalline Fe 5 Si 3 . As a result, an intrinsically broader entropy change over a larger temperature span is generated in the lightly doped single crystal of Fe 5 Si 3 . The magnetic moment of the system is also enhanced. Density functional theory (DFT) calculations are performed to gain microscopic insights into the experimental findings. The results suggest that the hexagonal Fe 5 Si 3 is a new giant room temperature MCE material that is on par with La–Fe–Si and Fe‐Mn‐P‐Si systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Future projections and uncertainty assessment of precipitation extremes in the Korean peninsula from the CMIP5 ensemble

Abstract Projections of changes in extreme climate are sometimes predicted by multimodel ensemble methods that combine forecasts from individual simulation models using weighted averaging. One method to assign weight to each model is the Bayesian model averaging (BMA) in which posterior probability is used. For the cases of extreme climate, the generalized extreme value distribution (GEVD) is typically used. We applied the approach of GEV‐embedded BMA to a series of 35 years of the annual maximum daily precipitation data (both historical data and data gathered from simulation experiments for future periods) over the Korean peninsula as simulated by the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Simulation data under two Representative Concentration Pathway (RCP) scenarios, namely RCP4.5 and RCP8.5, were used. Observed data and 17 CMIP5 models for 12 gird cells in Korea have been examined to predict future changes in precipitation extremes. A simple regional frequency analysis of pooling observations from three stations in each cell was employed to reduce the estimation variance and local fluctuations. A bias correction technique using the regression‐type transfer function was applied to these simulation data. Return levels spanning over 20 and 50 years, as well as the return periods relative to the reference years (1971–2005), were estimated for two future periods, namely Period 1 (2021–2050) and Period 2 (2066–2095). From these analyses, relative increase observed in the spatially averaged 20‐year (50‐year) return level was approximately 23% (16%) and 45% (36%) in the RCP4.5 and RCP8.5 experiments, respectively, by the end of the 21st century. We concluded that extreme rainfalls will likely occur two times and four times more frequently in the RCP4.5 and RCP8.5 scenarios, respectively, as compared to in the reference years by the end of the 21st century.

Lee, Youngsaeng↗
DOE OSTI2020

Projected increase in compound dry and hot events over global land areas

Abstract Under global warming, dry and hot events have been increasing in recent decades and are projected to increase in the future across global land areas. The impacts of compound dry and hot events may lead to increased stress to the natural and human systems than separate dry or hot events. Thus, quantitative assessments of global land areas affected by these compound events are needed to understand their risks. This study focuses on the variation in global land and cropland areas affected by compound dry and hot events for both historical and future periods using observations from Climatic Research Unit (CRU) and simulations from Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. Based on historical observations and simulations, a substantial increase in the spatial extent of these compound events was detected, especially since the 1980s. Climate model projections under the Representative Concentration Pathway (RCP) 8.5 scenario reveal that both global land and cropland areas affected by compound dry and hot events will increase to approximately 1.7–1.8 times by the end of the 21st century. Based on different thresholds of compound events, the spatial extent of global land areas during the June–July–August (December–January–February) season will increase by 12.38–17.20% (7.83–11.19%) in 2050–2099 relative to that in 1950–1999, and the spatial extent of global cropland areas will increase by 14.69–19.63% (9.60–14.48%). The increase in areas affected by compound dry and hot events may lead to more losses in different sectors in the future and more efforts are needed to cope with their potential impacts.

Wu, Xinying↗
DOE OSTI2018

Reduced connection between the East Asian Summer Monsoon and Southern Hemisphere Circulation on interannual timescales under intense global warming

Previous studies show a close relationship between the East Asian Summer Monsoon (EASM) and Southern Hemisphere (SH) circulation on interannual timescales. In this study, we investigate whether this close relationship will change under intensive greenhouse-gas effect by analyzing simulations under two different climate background states: preindustrial era and Representative Concentration Pathway (RCP) 8.5 stabilization from the Community Climate System Model Version 4 (CCSM4). Results show a significantly reduced relationship under stabilized RCP8.5 climate state, such a less correlated EASM with the sea level pressure in the southern Indian Ocean and the SH branch of local Hadley Cell. Further analysis suggests that the collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to this warming leads to a less vigorous northward meridional heat transport, a decreased intertropical temperature contrast in boreal summer, which produces a weaker cross-equatorial Hadley Cell in the monsoonal region and a reduced Interhemispheric Mass Exchange (IME). Since the monsoonal IME acts as a bridge connecting EASM and SH circulation, the reduced IME weakens this connection. By performing freshwater hosing experiment using the Flexible Global Ocean—Atmosphere—Land System model, Grid-point Version 2 (FGOALS-g2), we show a weakened relationship between the EASM and SH circulation as in CCSM4 when AMOC collapses. Our results suggest that a substantially weakened AMOC is the main driver leading to the EASM, which is less affected by SH circulation in the future warmer climate.

Meteorology & Atmospheric Sciences↗
DOE OSTI2020

A new spatially distributed added value index for regional climate models: the EURO-CORDEX and the CORDEX-CORE highest resolution ensembles

The added value of using regional climate models (RCMs) to downscale data from general circulation models (GCMs) has often been questioned and researched. Although several studies have used different methods to identify (and in some cases quantify) the added value, there is still a need to find a general metric that quantifies the added value of any variable. This paper builds on past studies to propose a new metric of added value in the simulation of present-day climate which measures the difference in the probability density functions (PDFs) at each grid-cell between a model and an observation source, and then compares the results of the RCM and GCM in order to spatially compute the added value index. The same method is also adapted to quantify the climate change downscaling signal in a way that is consistent with the present-day metric. These new metrics are tested on the daily precipitation output from the EURO-CORDEX and CORDEX-CORE projection ensembles and reveal an overall positive added value of RCMs, especially at the tail-end of the distribution. Higher added value is obtained in areas of complex topography and coast-lines, as well as in tropical regions. Areas with large added value in present-day climate are consistent with areas of significant climate change downscaling signal in the RCP 8.5 far future simulations, and when the analysis is repeated at a low-resolution. The use of different resolution observations shows that the added value tends to decrease when models are compared to low-resolution observation datasets.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Spatially resolved estimation of ozone-related mortality in the United States under two representative concentration pathways (RCPs) and their uncertainty

We report that the spatial pattern of the uncertainty in air pollution-related health impacts due to climate change has rarely been studied due to the lack of high-resolution model simulations, especially under the Representative Concentration Pathways (RCPs), the latest greenhouse gas emission pathways. We estimated future tropospheric ozone (O 3 ) and related excess mortality and evaluated the associated uncertainties in the continental United States under RCPs. Based on dynamically downscaled climate model simulations, we calculated changes in O 3 level at 12 km resolution between the future (2057 and 2059) and base years (2001–2004) under a low-to-medium emission scenario (RCP4.5) and a fossil fuel intensive emission scenario (RCP8.5). We then estimated the excess mortality attributable to changes in O 3 . Finally, we analyzed the sensitivity of the excess mortality estimates to the input variables and the uncertainty in the excess mortality estimation using Monte Carlo simulations. O 3 -related premature deaths in the continental U.S. were estimated to be 1312 deaths/year under RCP8.5 (95 % confidence interval (CI): 427 to 2198) and ₋2118 deaths/year under RCP4.5 (95 % CI: ₋3021 to ₋1216), when allowing for climate change and emissions reduction. The uncertainty of O 3 -related excess mortality estimates was mainly caused by RCP emissions pathways. Finally, excess mortality estimates attributable to the combined effect of climate and emission changes on O 3 as well as the associated uncertainties vary substantially in space and so do the most influential input variables. Spatially resolved data is crucial to develop effective community level mitigation and adaptation policy.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2016

Simulated differences in 21st century aridity due to different scenarios of greenhouse gases and aerosols

Aridity, defined as the ratio of precipitation (P) to potential evapotranspiration (PET) over land, is critical to natural ecosystems and agricultural production. Global climate models project global decreases of P/PET (drying) in the 21st century. We examine the uncertainty of aridity projections due to scenarios of greenhouse gases (GHGs) and aerosols with three sets of ensemble simulations from a single climate model, the Community Earth System Model (CESM1). Ensembles consist of two Radiative Concentration Pathways (RCPs) and a scenario with RCP-like GHGs but with aerosol precursor emissions and atmospheric oxidants fixed at the year 2005 level. Under a high GHGs emission scenario (RCP8.5), global land P/PET decreases (drying) by 6.4 ± 0.8 % in 2060–2080 relative to 1985–2005. A GHG mitigation scenario (RCP4.5) would reduce the drying (P/PET decrease) to 3.7 ± 0.6 %. Although future aerosol emissions reduction would increase P, we find that it has little impact on global aridity due to offsetting effects on PET. Regionally, deceasing aerosols can have significant effects and aerosol-induced P/PET changes are due to different factors across different regions. When normalized by global mean temperature response, GHGs decrease global land P/PET by 2.7 ± 0.6 %/°C and surface temperature changes dominate GHG-induced P/PET change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Future hurricane storm surge risk for the U.S. gulf and Florida coasts based on projections of thermodynamic potential intensity

Coastal populations in the global tropics and sub-tropics are vulnerable to the devastating impacts of hurricane storm surge and this risk is only expected to rise under climate change. In this study, we address this issue for the U.S. Gulf and Florida coasts. Using the framework of Potential Intensity, observations and output from coupled climate models, we show that the future large-scale thermodynamic environment may become more favorable for hurricane intensification. Under the RCP 4.5 emissions scenario and for the peak hurricane season months of August–October, we show that the mean intensities of Atlantic hurricanes may increase by 1.8–4.2 % and their lifetime maximum intensities may increase by 2.7–5.3 % when comparing the last two decades of the 20th and 21st centuries. We then combine our estimates of hurricane intensity changes with projections of sea-level rise to understand their relative impacts on future storm surge using simulations with the National Weather Service’s SLOSH (Sea, Lake, and Overland Surges from Hurricanes) model for five historical hurricanes that made landfall in the Gulf of Mexico and Florida. Considering uncertainty in hurricane intensity changes and sea-level rise, our results indicate a median increase in storm surge ranging between 25 and 47 %, with changes in hurricane intensity increasing future storm surge by about 10 % relative to the increase that may result from sea level rise alone, with highly non-linear response of population at risk.

Climate change↗
DOE OSTI2018

Investigation of Magnetic, Magnetocaloric, and Critical Properties of La{sub 0.5}Ba{sub 0.5}MnO{sub 3} Manganite

We present an extensive study of the magnetic properties of a novel La{sub 0.5}Ba{sub 0.5}MnO{sub 3} perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μ{sub o}H) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (|ΔS{sub M}{sup max}|) took a value of 1.4 J kg{sup − 1} K{sup − 1} at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (T{sub C}). This large entropy change might be instigated from the abrupt reduction of magnetization at T{sub C}. The magnetocaloric effect (MCE) is maximum at T{sub C} as represented by M (μ{sub o}H) isotherms. The relative cooling power (RCP) is 243.2 J kg{sup − 1} at μ{sub o}H = 4.0 T. Moreover, the critical properties near T{sub C} have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < T{sub C} and the other for T > T{sub C}, signifying that the critical exponents obtained in this work are accurate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr{sub 1−x}Pb{sub x}Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the T{sub C} are determined as 286, 280 and 278 K for x= 0.4, 0.5 and 0.6 in Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔS{sub M}) value. −ΔS{sub M} values are found as 3.68, 3.15 and 2.85 J kg{sup − 1} K{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Study of Magnetocaloric Effect on Strontium Ferrite SrFe{sub 12}O{sub 19} Ceramic

Magnetocaloric effect on SrFe{sub 12}O{sub 19} ceramic have been studied using Monte Carlo simulation. The thermal magnetization, dM/dT, magnetic entropy, and the specific heat of SrFe{sub 12}O{sub 19} ceramic are obtained for several magnetic fields. The temperatures dependence of the magnetic entropy and of the adiabatic temperature for a several magnetic field have been obtained. The field dependence of relative cooling power (RCP) of SrFe{sub 12}O{sub 19} ceramic has been determined for a several magnetic fields. The magnetic hysteresis cycle of SrFe{sub 12}O{sub 19} ceramic has been obtained for a several temperatures. The obtained values are close to the experimental values. The transition paramagnetic to ferromagnetic is found at the Curie temperature. The second phase transition is also obtained around the Curie temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructural, Magnetic, Magnetocaloric, and Electrical Properties of Ni{sub 0.4}Mg{sub 0.3}Cu{sub 0.3}Fe{sub 2}O{sub 4} Ferrite Prepared Using Sol–Gel Method

Detailed investigations of the microstructural, magnetic, magnetocaloric, and electrical properties of Ni{sub 0.4}Mg{sub 0.3}Cu{sub 0.3}Fe{sub 2}O{sub 4} ferrite synthesized by sol-gel method have been investigated. XRD pattern indicates that sample has cubic spinel structure with Fd 3-bar m symmetry. The cation distribution of the sample has been determined by Rietveld refinement. Temperature dependence of magnetization shows that sample exhibits a second-order PM to FM phase transition at the Curie temperature T{sub C} = 690 K. From the M(μ{sub 0}H,T) data, we found that the maximum entropy change |ΔS{sub M}{sup max}| reaches value of about 1.56 J kg{sup − 1} K{sup − 1} and relative cooling power (RCP) of 136 J kg{sup − 1} at μ{sub 0}H = 5 T. From electrical conductivity curves, the estimated value of the activation energy is equal to 0.349 eV. The Nequist diagram at different temperatures reveals that the grain boundary contribution is responsible to the conduction process for the studied sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Non-magnetic Ti{sup 4+} Ion Doping at Mn Site on Structural, Magnetic, and Magnetocaloric Properties of La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3}Mn{sub 1−x}Ti{sub x}O{sub 3} Manganites (x = 0.0 and 0.1)

Polycrystalline perovskite AMn{sub 1−x}TiO{sub 3} with A = La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3} (x = 0.0 and 0.1) have been prepared using solid-state reaction method. X-ray powder diffraction and Rietveld refinement revealed that all samples crystallize in a rhombohedral structure with space group R 3-bar c From M–T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. The Curie temperature (T{sub C}) decreases from 280 to 123 K when the percentage of Ti increases to 10%. The values of the magnetization M(H) decrease when increasing the Ti content. Moreover, the magnetocaloric effect (MCE) was estimated in terms of isothermal entropy change (−ΔS{sub M}) using the M(T, μ{sub 0}H) data and employing the thermodynamic Maxwell equation. In addition, using a phenomenological model, we determine magnetocaloric effect from the calculation of magnetization as a function of temperature under different external magnetic fields. Also, we can determine the relative cooling power (RCP) and the specific heat which varies from 2.803 to 7.354 J/(kg/K) for the undoped sample from M(T, μ{sub 0}H) data at different magnetic fields theoretically.

36 MATERIALS SCIENCE↗