20 research outputs found
Characterization of electron and phonon transports in Bi-doped CaMnO3 for thermoelectric applications
Electron and phonon transports in CaMnO3 and its Bi-doped counterpart,
Bi0.03Ca0.97MnO3, are investigated by thermoelectric transport measurements,
Raman spectroscopy, and first-principles calculations. In particular, we focus
on CaMnO3 and Bi0.03Ca0.97MnO3's electronic structures, temperature-dependent
electron and phonon lifetimes, and their sound velocities. We find that the
anti-ferromagnetic insulator CaMnO3 breaks the Wiedemann-Franz (WF) law with
the Lorenz number reaching four times that of ordinary metals at room
temperature. Bismuth doping reduces both the electrical resistivity and the
Seebeck coefficient of CaMnO3, thus it recovers the WF law behavior. Raman
spectroscopy confirms that Bi0.03Ca0.97MnO3 has a lower Debye frequency as well
as a shorter phonon lifetime. As a result, Bi0.03Ca0.97MnO3 exhibits superior
thermoelectric properties over the pristine CaMnO3 due to the lower thermal
conductivity and electronic resistivity.Comment: 7 pages, 7 figure
Investigation of electron and phonon transport in Bi-doped CaMnO3 for thermoelectric applications
The electron and phonon transports in CaMnO3 and in one of its Bi-doped counterparts, namely,
Bi0.03Ca0.97MnO3, are investigated using the thermoelectric transport measurements and first-principles calculations. We find that antiferromagnetic insulator CaMnO3 breaks the Wiedemann–Franz law with the Lorenz number reaching four times that of ordinary metals at room temperature. Bismuth doping reduces both the electrical resistivity and Seebeck coefficient of CaMnO3; thus, it recovers the Wiedemann–Franz law behavior. In addition, Bi0.03Ca0.97MnO3 possesses a shorter phonon lifetime according to the transport measurements. As a result, Bi0.03Ca0.97MnO3 exhibits superior thermoelectric properties over pristine CaMnO3 owing to the lower thermal conductivity and electrical resistivity
Spin-tunable thermoelectric performance in monolayer chromium pnictides
Historically, finding two-dimensional (2D) magnets is well known to be a
difficult task due to instability against thermal spin fluctuations. Metals are
also normally considered poor thermoelectric (TE) materials. Combining
intrinsic magnetism in two dimensions with conducting properties, one may
expect to get the worst for thermoelectrics. However, we will show this is not
always the case. Here, we investigate spin-dependent TE properties of monolayer
chromium pnictides (CrX, where X = P, As, Sb, and Bi) using first-principles
calculations of electrons and phonons, along with Boltzmann transport formalism
under energy-dependent relaxation time approximation. All the CrX monolayers
are dynamically stable and they also exhibit half metallicity with
ferromagnetic ordering. Using the spin-valve setup with antiparallel spin
configuration, the half metallicity and ferromagnetism in monolayer CrX enable
manipulation of spin degrees of freedom to tune the TE figure of merit (ZT). At
optimized chemical potential and operating temperature of 500 K, the maximum ZT
values (= 0.22, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs,
CrSb, and CrBi improve up to almost twice the original values (ZT = 0.12, 0.08,
and 0.05) without the spin-valve configuration. Only in CrP, which is the
lightest species and less spin-polarized among CrX, the maximum ZT (= 0.34)
without the spin-valve configuration is larger than that (= 0.19) with the
spin-valve one. We also find that, at 500 K, all the CrX monolayers possess
exceptional TE power factors of about 0.02-0.08 W/m.K2, which could be one of
the best values among 2D conductors.Comment: 7 pages, 6 figure