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Sharma A, Rangra VS. Hydrogenation driven ultra-low lattice thermal conductivity in β12borophene. J Phys Condens Matter 2024; 36:205704. [PMID: 38335552 DOI: 10.1088/1361-648x/ad2800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Accepted: 02/09/2024] [Indexed: 02/12/2024]
Abstract
Borophene gathered large interest owing to its polymorphism and intriguing properties such as Dirac point, inherent metallicity, etc but oxidation limits its capabilities. Hydrogenated borophene was recently synthesised experimentally to harness its applications. Motivated by experimental work, in this paper, using first-principles calculations and Boltzmann transport theory, we study the freestandingβ12borophene nanosheet doped and functionalised with hydrogen (H), lithium (Li), beryllium (Be), and carbon (C) atoms at differentβ12lattice sites. Among all possible configurations, we screen two stable candidates, pristine and hydrogenatedβ12borophene nanosheets. Both nanosheets possess dynamic and mechanical stability while the hydrogenated sheet has different anisotropic metallicity compared to pristine sheet leading to enhancement in brittle behaviour. Electronic structure calculations reveal that both nanosheets host Dirac cones (DCs), while hydrogenation leads to shift and enhancement in tilt of the DCs. Further hydrogenation leads to the appearance of additional Fermi pockets in the Fermi surface. Transport calculations reveals that the lattice thermal conductivity changes from 12.51 to 0.22 W m-1 K-1(along armchair direction) and from 4.42 to 0.07 W m-1 K-1(along zigzag direction) upon hydrogenation at room temperature (300 K), demonstrating a large reduction by two orders of magnitude. Such reduction is mainly attributed to decreased phonon mean free path and relaxation time along with the enhanced phonon scattering rates stemming from high frequency phonon flat modes in hydrogenated nanosheet. Comparatively larger weighted phase space leads to increased anharmonic scattering in hydrogenated nanosheet contributing to ultra-low lattice thermal conductivity. Consequently, hydrogenatedβ12nanosheet exhibits a comparatively higher thermoelectric figure of merit (∼0.75) at room temperature along armchair direction. Our study demonstrates the effects of functionalisation on transport properties of freestandingβ12borophene nanosheets which can be utilised to enhance the thermoelectric performance in two-dimensional (2D) systems and expand the applications of boron-based 2D materials.
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Affiliation(s)
- Ashish Sharma
- Department of Physics, Himachal Pradesh University, Summer Hill, Shimla, Himachal Pradesh 171005, India
| | - Vir Singh Rangra
- Department of Physics, Himachal Pradesh University, Summer Hill, Shimla, Himachal Pradesh 171005, India
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Thakur M, Vij A, Singh F, Rangra VS. Spectroscopic studies of metastable tetragonal ZrO 2 nanocrystals. Spectrochim Acta A Mol Biomol Spectrosc 2024; 305:123495. [PMID: 37827001 DOI: 10.1016/j.saa.2023.123495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Revised: 09/29/2023] [Accepted: 10/03/2023] [Indexed: 10/14/2023]
Abstract
This study delves into an examination of the structural and luminescent properties of zirconium dioxide (ZrO2) synthesized via the solid-state combustion method. Nitrates are harnessed as the oxidizing agent, while glycine serves as the fuel. Two distinct compositions are explored: a stoichiometric 1:1 ratio and a fuel-enriched 1:2 ratio. The structural analysis, employing X-ray diffraction and Raman spectroscopy, predominantly manifests a tetragonal structural phase in both samples; however, a minor monoclinic phase has also been observed in the former sample. The band gap was found to be 4.50 eV and 4.28 eV for ZrO2 synthesized in stoichiometric ratio and a fuel-enriched ratio respectively. The samples also show defects assisted photoluminescence in both the samples. The thermoluminescence of samples were investigated after irradiating the samples with UV and gamma rays for different doses. The TL curves manifest a shift towards lower temperatures at higher doses. . Significantly, the sample prepared with a 1:1 nitrate-fuel ratio exhibits a more pronounced overall TL intensity. In conclusion, our findings imply that the formation of the tetragonal phase may be influenced by strain energy, rather than being solely ascribed to size effects and oxygen vacancies within the lattice.
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Affiliation(s)
- Maneshwar Thakur
- Department of Physics, Himachal Pradesh University, Shimla 171005, India
| | - Ankush Vij
- Department of Physics & Astrophysics, Central University Haryana, Mahendergarh 123031, India.
| | - Fouran Singh
- Materials Science Group, Inter- University Accelerator Centre, New Delhi 110067, India
| | - Vir Singh Rangra
- Department of Physics, Himachal Pradesh University, Shimla 171005, India.
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Sharma A, Rangra VS. Electronic and elastic correlations in AlB 2-type two-dimensional hexagonal MBenes. J Phys Condens Matter 2023. [PMID: 38052100 DOI: 10.1088/1361-648x/ad1291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
With the advent of MXenes as two-dimensional (2D) materials beyond graphene, non carbonic 2D materials analogically referred as MBenes have significantly attracted researchers' attention. Such 2D MBenes remains largely unexplored. Here, we systematically investigate electronic and elastic properties of two-dimensional transition metal based AlB2-type hexagonal MBenes consisting of a honeycomb networked graphene like boron layer embedded with diverse transition metal atoms at centre. First we determine the thermodynamic, dynamic, thermal, and mechanical stability of MBenes, considering a wide range of 3d, 4d, and 5d transition metal elements. Electronic and elastic calculations are performed for stable MBenes in order to parameterize and investigate the interdependence of properties. Elastic calculations predicts the brittle-ductile nature and bond character of MBenes while unravelling the in-plane auxetic behaviour. Our electronic calculations predict the metallic band nature for 2D VB2, NbB2, TaB2, and WB2alongwith previously reported dirac points in 2D TiB2, FeB2, ZrB2, and HfB2. The elastic and electronic calculations clearly indicates the non-directional metallic bonds and intrinsically ductile nature of 2D-FeB2distinct from other MBenes. Subsequently we performed a covariance analysis to assess the correlation amongst the observables of interest and further establish the interdependence of the properties. Our calculations for elastic correlations also suggests that mechanical brittle-ductile nature and auxetic behaviour of MBenes can be tuned by strain engineering of the elastic constants. Our results further suggests that strong correlations between poisson ratio and d state electrons can be utilised to tune the auxetic behaviour by careful doping of the materials. Our work demonstrates the weak elastic-electronic correlations, suggesting that the strain engineering can be utilised for the tailored behaviour of MBenes for practical applications. Thus, our systematic analysis of the mechano-elastic and electronic properties of 2D hexagonal MBenes and their correlations advance our understandings of emergent 2D family.
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Affiliation(s)
- Ashish Sharma
- Physics, Himachal Pradesh University, Room No. 105, Himachal Pradesh University, SummerHill, Shimla, HP, Shimla, Himachal Pradesh, 171005, INDIA
| | - Vir Singh Rangra
- Physics, Himachal Pradesh University, Department of Physics, Himachal Pradesh University, SummerHill, Shimla, HP, Shimla, Himachal Pradesh, 171005, INDIA
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Sharma A, Thakur A, Rangra VS. Excitonic effects on the optical spectra of TiB 2nanosheets. J Phys Condens Matter 2023; 36. [PMID: 37832563 DOI: 10.1088/1361-648x/ad0353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 10/13/2023] [Indexed: 10/15/2023]
Abstract
Two-dimensional (2D) transition metal borides, have recently attracted tremendous interest and become an emerging class of 2D materials due to their intriguing properties. We report systematic investigation of stability, electronic properties and optical activity of 2D-TiB2nanosheets using first-principles calculations. By combining elastic and phonon-dispersion calculations, we substantiated the mechanical and dynamic stability of 2D-TiB2nanosheets. Our results of elastic calculations reveal that addition of an extra layer destroys the auxetic behaviour of monolayer (ML) 2D-TiB2with significant reduction in the brittleness. Further, based on the spin-polarised electronic structure calculations, we find that a low-dimensional metallic state of ML can be achieved by tuning the distance between the titanium and boron layers. The calculations clearly reveal that metallic nature does not destroys the auxetic behaviour of ML. Subsequently, we investigated the optical response of 2D-TiB2nanosheets (ML and bilayer (BL)) at the level of density functional theory and many-body perturbation theory. The results obtained by solving Bethe-Salpeter equation (GW+BSE formalism) shows that excitonic effects causes a slight blue-shift in the absorption spectra of the nanosheets with ML being optically active with sharp peaks in infrared (IR) and ultraviolet (UV) regions while BL shows the reduced optical activity across wide range of photon energies spanning the near-IR to UV region. In addition, electronic polarisability of the nanosheet decreases with addition of another layer in ML 2D-TiB2. Further investigation of transition probabilities clearly indicates that the response of ML at Dirac point is tunable by spin-orbital coupling effects which makes these nanosheets promising for spintronic applications. The BL exhibits distinct electronic, and optical properties compared to ML. Our study unravels the structural, elastic, electronic, and optical properties of 2D-TiB2nanosheets and suggests them as promising candidate for variety of optoelectronic and spintronic applications.
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Affiliation(s)
- Ashish Sharma
- Department of Physics, Himachal Pradesh University, Summer Hill, Shimla, Himachal Pradesh 171005, India
| | - Anupma Thakur
- Department of Mechanical & Energy Engineering, Purdue School of Engineering & Technology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, United States of America
| | - V S Rangra
- Department of Physics, Himachal Pradesh University, Summer Hill, Shimla, Himachal Pradesh 171005, India
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Thakur M, Vij A, Kumar A, Koo BH, Singh F, Rangra VS. Electronic structure and defects induced luminescence study of phase stabilized t-ZrO 2 nanocrystals. LUMINESCENCE 2023. [PMID: 37056200 DOI: 10.1002/bio.4505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 04/02/2023] [Accepted: 04/10/2023] [Indexed: 04/15/2023]
Abstract
Luminescent tetragonal-ZrO2 nanocrystals were synthesized using an optimized combustion method without post-synthesis annealing and characterized using X-ray diffraction, electron microscopy, Raman, X-ray photoelectron spectroscopy, UV-Visible, photoluminescence spectroscopy, thermoluminescence and vibrating sample magnetometry. The as synthesized t-ZrO2 nanocrystals have a band gap of 4.65 eV and exhibit defect assisted blue emission (CIE coordinates 0.2294,0.1984) when excited with 270 nm. The defect states were qualitatively and quantitatively analyzed using thermoluminescence (TL) after irradiating nanocrystals with gamma and UV radiation at various doses. The TL glow curves show intense emission in the high temperature region from 523-673 K for both UV and gamma irradiated samples; however, another less intense TL peak was also observed in the low temperature region from 333-453 K with gamma irradiation at higher doses, indicating the formation of shallow trapping states. The activation energies, frequency factor and order of kinetics were estimated through the computerized glow curve deconvolution method for the shallow and deep traps for γ and UV- irradiated samples. The present study shows that phase stabilized t-ZrO2 nanocrystals are potential candidates for luminescence-based applications.
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Affiliation(s)
- Maneshwar Thakur
- Department of Physics, Himachal Pradesh University, Shimla, India
| | - Ankush Vij
- Department of Physics, University of Petroleum and Energy Studies (UPES) Dehradun, India
- Department of Physics & Astrophysics, Central University Haryana, Mahendergarh, India
| | - Akshay Kumar
- Department of Material Science and Engineering, Changwon National University, Changwon, Gyeongnam, Republic of Korea
| | - Bon Heun Koo
- Department of Material Science and Engineering, Changwon National University, Changwon, Gyeongnam, Republic of Korea
- Department of Materials Convergence and System Engineering, Changwon National University, Changwon, Gyeongnam, Republic of Korea
| | - Fouran Singh
- Materials Science Group, Inter- University Accelerator Centre, New Delhi, India
| | - Vir Singh Rangra
- Department of Physics, Himachal Pradesh University, Shimla, India
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