Defects assisted luminescence in m-HfO2 nanocrystals: An experimental and theoretical study

Kumar, Rajesh; Vij, Ankush; Singh, Mukhtiyar

doi:10.1016/j.ijleo.2021.168121

Cited by 9 publications

(9 citation statements)

References 34 publications

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“…The estimated value of the band gap using GGA and TB-mBJ is listed in table 2. The calculated band gaps using TB-mBJ potential are in good agreement with the previously available experimental and theoretical results [22,23,44,51]. From the band structures, it can be seen that the top of the valance band (VB) for m-, o-, and t-phases are at Γ the point, and in the c-phase is at X point.…”

Section: Electronic Propertiessupporting

confidence: 86%

“…The structural parameters are optimized for all the polymorphs of HfO 2 within the parameterization of GGA by fitting Birch-Murnaghan equation of states [49], and the corresponding volume optimization curves are shown in figure 1. Our optimized lattice parameters are in good agreement with the previously reported experimental results (listed in table 1) [22][23][24][25]. Therefore, we have not optimized angles of the monoclinic structure but rather taken the experimental values from literature [22].…”

Section: Structural Propertiessupporting

confidence: 86%

“…Our optimized lattice parameters are in good agreement with the previously reported experimental results (listed in table 1) [22][23][24][25]. Therefore, we have not optimized angles of the monoclinic structure but rather taken the experimental values from literature [22].…”

Section: Structural Propertiessupporting

confidence: 86%

“…The VB maxima of o-HfO 2 (inset figure 4) is shown in inset for its better appearance. Hence the phases c-, o-, and t-HfO 2 show the direct band gap, whilst m-HfO 2 exhibits an indirect band gap which has been experimentally verified in a recent study by Kumar et al [22].…”

Section: Electronic Propertiessupporting

confidence: 64%

“…The synthesis temperatures vary significantly for different polymorphs of HfO 2 . A low temperature thermodynamically stable monoclinic (m) phase exists at ∼1200 • C, whilst tetragonal (t) phase and cubic (c) phase occurs, respectively, at 1700 • C and 2500 • C [22][23][24]. The high pressure transforms the m-HfO 2 to orthorhombic (o) phase [25].…”

Section: Introductionmentioning

confidence: 99%

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Carrier concentration mediated enhancement in thermoelectric performance of various polymorphs of hafnium oxide: a plausible material for high temperature thermoelectric energy harvesting application

Kumar¹,

Kumar²,

Singh³

et al. 2022

J. Phys. D: Appl. Phys.

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The optimization of figure of merit by tuning carrier concentrations is an effective way to realize efficient thermoelectrics. Recently, the feasibility of high p-type carrier concentration (order of ~1022 cm-3) is experimentally demonstrated in various polymorphs of HfO2. In light of these studies, using the first-principles calculation combined with the semi-classical Boltzmann transport theory and phonon dynamics, we realized high thermoelectric performance in various polymorphs of HfO2 in a range of carrier concentrations at high temperatures. The phonon dispersion calculations confirm the dynamical stability of all polymorphs. The observed values of the Seebeck coefficient are 945.27 mV/K, 922.62 mV/K, 867.44 mV/K, and 830.81 mV/K for tetragonal (t), orthorhombic (o), monoclinic (m), and cubic (c) phases of HfO2, respectively, at 300 K. These values remain positive at all studied temperatures which ensures the p-type behaviour of HfO2 polymorphs. The highest value of electrical conductivity 2.34×1020  -1m-1s-1observed in c-HfO2 at 1200 K, and the lowest value of electronic thermal conductivity (0.37×1015 W/mKsobserved in o-HfO2 at 300 K. The lattice thermal conductivities at room temperature are 5.56 W/mK, 2.87 W/mK, 4.32 W/mK, and 1.75 W/mK for c-, m-, o- and t- HfO2, respectively which decrease to 1.58 W/mK, 0.92 W/mK, 1.12 W/mK, 0.53 W/mK at 1200 K for respective phases. The low lattice thermal conductivities lead to the high values of the figure of merit, i.e., 0.97, 0.87, 0.83, and 0.77 at 1200 K for the m-, o-, t-, and c- HfO2, respectively, at the optimized carrier concentrations (~1021 cm-3). The predicted optimized carrier concentrations for various phases are in close agreement with the experimental reports. The estimated high figure of merit can make HfO2 a potential material for thermoelectric energy harvesting applications at elevated temperatures.

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Section: Electronic Propertiessupporting

confidence: 86%