Understanding Thermal Properties in Entropy Stabilized Oxides

Transcription

1 Understanding Thermal Properties in Entropy Stabilized Oxides Jeff Braun, 1 Ashutosh Giri, 1 Zsolt Rak, 2 Mina Lim, 2 Christina M. Rost, 2 Jon-Paul Maria, 2 Donald W. Brenner, 2 and Patrick E. Hopkins 1 1 Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904, USA 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA

2 Advanced materials (High Entropy Alloys) High Entropy Alloys (HEAs) are 5+ metal components containing high configurational entropy HEAs have been demonstrated to possess exceptional properties. For high temperature applications, HEAs are especially promising 2:30 today Heat transfer mechanisms in Hybrid superlattices

3 Why study Entropy Stabilized Oxides? Materials that can withstand temperatures above 2500 C in oxidizing conditions. Mixture of MgO, CoO, NiO, CuO, and ZnO that forms a single phase rocksalt crystal at high temperatures

4 Sample Description 5- and 6-component (300 nm) thin film samples: 5-C MgO 6-C MgO 5 oxide-component system (5-C) Equimolar mixture of MgO, CoO, NiO, CuO and ZnO Rocksalt Structure grown at 600 C lattice parameter of 4.29 Å 6 oxide-component system (6-C) Equimolar mixture of MgO, CoO, NiO, CuO, ZnO, and ScO Rocksalt Structure grown at 400 C lattice parameter of 4.18 Å

5 BiBO EOM Ti:Sapphire Laser 10X Objective Transducer ESO film MgO

6 Photodetector BiBO EOM Beam Splitter Ti:Sapphire Laser Lock-in Amplifier Delay Stage Dichroic Mirror 10X Objective Transducer ESO film MgO

7 Photodetector BiBO EOM Beam Splitter Ti:Sapphire Laser Lock-in Amplifier Delay Stage Transducer ESO film Dichroic Mirror 10X Objective TDTR ratio, -X /Y TDTR data, 117 nm Al/Si Thermal model 1 MgO Pump-probe time delay, (ps) Pump-probe time delay, (ns)

8 Photodetector BiBO EOM Beam Splitter Ti:Sapphire Laser Lock-in Amplifier Delay Stage Transducer ESO film Dichroic Mirror 10X Objective TDTR ratio, -X /Y TDTR data, 117 nm Al/Si Thermal model MgO Pump-probe time delay, (ps) Pump-probe time delay, (ns)

9 Photodetector BiBO EOM Beam Splitter Ti:Sapphire Laser Lock-in Amplifier Delay Stage Transducer ESO film MgO Dichroic Mirror 10X Objective Can measure thermal conductivity of thin films and substrates (k) separately from thermal boundary conductance Nanometer spatial resolution (~10 s of nm) Femtosecond to nanosecond temporal resolution Noncontact Typically, can fit for two parameters

10 Photodetector BiBO EOM Beam Splitter Ti:Sapphire Laser Lock-in Amplifier Delay Stage Transducer ESO film Dichroic Mirror 10X Objective parameters in thermal model [C 1 κ 1 d 1 ] h 1 [C 2 κ 2 d 2 ] 4 unknown parameters in model MgO h 2 [C 3 κ 3 d 3 ]

11 Using modulation frequency to improve sensitivity Modulation frequency, f Pump Probe 12.5 ns btw pulses un-modulated Changing modulation frequency can change parameters to which thermal model is sensitive Combined FDTR/TDTR approach allows for fitting multiple parameters Metal film transducer Thin film Substrate Thermal penetration depth Measurement volume TDTR Reviews and Analyses Rev. Sci. Instr. 75, 5119 Rev. Sci. Instr. 79, J. Heat Trans. 132, Ann. Rev. Heat Trans. 16, 159

12 Measuring Heat Capacity and Thermal Conductivity (300 K) Sensitivity to Ratio Sensitivity to Phase f = 10 MHz Time (ns) t = 500 ps -5 Heat Capacity Al/ESO TBC -10 ESO/MgO TBC Thermal Conductivity Frequency (MHz) Time-domain shows sensitivity to 3 parameters, but unable to decouple heat capacity from thermal conductivity Frequency-domain shows sensitivity to all 4 parameters, and able to decouple heat capacity from thermal conductivity

13 Heat Capacity Heat capacity of alloys and solid solutions is often taken from literature data for bulk properties of constituent materials Heat Capacity (MJ m -3 K -1 ) MgO CoO NiO CuO ZnO Rule of mixtures: [(J) / (mol K)] Temperature (K) [(J) / (m 3 K)]

14 Heat Capacity Heat capacity of alloys and solid solutions is often taken from literature data for bulk properties of constituent materials 5 Rule of mixtures: 4 Heat Capacity (MJ m -3 K -1 ) C prediction with rule of mixtures 6-C 5-C [(J) / (mol K)] Temperature (K) [(J) / (m 3 K)]

15 Thermal conductivity (k) 20 CuO 0.2 NiO 0.8 Thermal Conductivity (W m -1 K -1 ) CoO 0.25 NiO componenet ESO ZnO 0.4 MgO component ESO Temperature (K) More disorder Lower k 5-C: Mg x Ni x Co x Cu x Zn x O 6-C: 5-C+Sc

16 Scattering mechanisms affecting alloys Mass impurity scattering in Si x Ge 1-x films Rigorously vetted over time Can mass impurity explain the decrease from the 5C to the 6C system? R. Cheaito et. al., PRL, 109 (2012)

17 Thermal conductivity (k) Thermal Conductivity (W m -1 K -1 ) MgO bulk model MgO 300 nm model 5/6-component model CoO 0.25 NiO component ESO ZnO 0.4 MgO component model MgO 300 nm 40% Zn model CuO 0.2 NiO componenet ESO 1 MgO Minimum Limit Temperature (K)

18 Acknowledgements

19 Thermal conductivity (k) model MgO Dispersion Parlinski, K., J. Łażewski, and Y. Kawazoe. "Ab initio studies of phonons in MgO by the direct method including LO mode." Journal of Physics and Chemistry of Solids 61.1 (2000): Abeles, B. "Lattice thermal conductivity of disordered semiconductor alloys at high temperatures." Physical Review (1963). Klemens, P. G. "The scattering of low-frequency lattice waves by static imperfections." Proceedings of the Physical Society. Section A (1955): 1113.