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ABSTRACT Phase competition underlies many remarkable and technologically important phenomena in transition metal oxides. Vanadium dioxide (VO2) exhibits a first-order metal–insulator

transition (MIT) near room temperature, where conductivity is suppressed and the lattice changes from tetragonal to monoclinic on cooling. Ongoing attempts to explain this coupled structural

and electronic transition begin with two alternative starting points: a Peierls MIT driven by instabilities in electron–lattice dynamics and a Mott MIT where strong electron–electron

correlations drive charge localization1,2,3,4,5,6,7,8,9,10. A key missing piece of the VO2 puzzle is the role of lattice vibrations. Moreover, a comprehensive thermodynamic treatment must

integrate both entropic and energetic aspects of the transition. Here we report that the entropy driving the MIT in VO2 is dominated by strongly anharmonic phonons rather than electronic

contributions, and provide a direct determination of phonon dispersions. Our _ab initio_ calculations identify softer bonding in the tetragonal phase, relative to the monoclinic phase, as

the origin of the large vibrational entropy stabilizing the metallic rutile phase. They further reveal how a balance between higher entropy in the metal and orbital-driven lower energy in

the insulator fully describes the thermodynamic forces controlling the MIT. Our study illustrates the critical role of anharmonic lattice dynamics in metal oxide phase competition, and

provides guidance for the predictive design of new materials. Access through your institution Buy or subscribe This is a preview of subscription content, access via your institution ACCESS

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institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS ORBITAL-SELECTIVE MOTT AND PEIERLS TRANSITION IN H_X_VO2 Article Open access 23

September 2022 MAGNETIC-FIELD-INDUCED INSULATOR–METAL TRANSITION IN W-DOPED VO2 AT 500 T Article Open access 17 July 2020 INSULATOR-TO-METAL TRANSITION IN ULTRATHIN RUTILE VO2/TIO2(001)

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ACKNOWLEDGEMENTS Research by J.D.B., O.D., M.E.M., E.D.S., L.A.B. and R.J.M. was supported by the US Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and

Engineering Division (MSED). Research by J.H. was supported by the Center for Accelerating Materials Modeling, funded by the US DOE, BES, MSED. Experimental work by C.W.L. was sponsored by

the Laboratory Directed Research and Development Program of ORNL (Principal Investigator, O.D.). Research by D.L.A. at the Spallation Neutron Source and J.Z.T., A.H.S. and B.M.L. at the

Advanced Photon Source (APS), Argonne National Laboratory (ANL), was supported by the US DOE, BES, Scientific User Facilities Division. We thank A. Tselev, S. Nagler, A. Banerjee, H.

Krakauer and V. Cooper for interesting discussions on VO2. Inelastic neutron scattering measurements were performed using the ARCS facility at the ORNL Spallation Neutron Source, which is

sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. We thank J. Niedziela for help with the sample environment at ARCS. IXS

measurements were performed using the X-ray Operations and Research (XOR) beamline 30-ID (HERIX) at the APS. Diffuse X-ray scattering measurements were performed using the XOR beamline

33-BM-C at the APS. We thank J. Karapetrova and C. Schleputz for assistance in setting up experiments at UNICAT. Use of the APS, an Office of Science User Facility operated for the US DOE

Office of Science by ANL, was supported by the US DOE under contract no. DE-AC02-06CH11357. Theoretical calculations were performed using resources of the National Energy Research Scientific

Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231. We thank O. Hellman for

providing the temperature-dependent effective potential software and assistance. AUTHOR INFORMATION Author notes * John D. Budai and Jiawang Hong: These authors contributed equally to this

work. AUTHORS AND AFFILIATIONS * Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, 37831, Tennessee, USA John D. Budai, Jiawang Hong, Michael E. Manley, 

Eliot D. Specht, Chen W. Li, Lynn A. Boatner & Olivier Delaire * Advanced Photon Source, Argonne National Laboratory, Argonne, 60439, Illinois, USA Jonathan Z. Tischler, Ayman H. Said 

& Bogdan M. Leu * Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, 37831, Tennessee, USA Douglas L. Abernathy * Neutron Sciences Directorate, Oak Ridge

National Laboratory, Oak Ridge, 37831, Tennessee, USA Robert J. McQueeney Authors * John D. Budai View author publications You can also search for this author inPubMed Google Scholar *

Jiawang Hong View author publications You can also search for this author inPubMed Google Scholar * Michael E. Manley View author publications You can also search for this author inPubMed 

Google Scholar * Eliot D. Specht View author publications You can also search for this author inPubMed Google Scholar * Chen W. Li View author publications You can also search for this

author inPubMed Google Scholar * Jonathan Z. Tischler View author publications You can also search for this author inPubMed Google Scholar * Douglas L. Abernathy View author publications You

can also search for this author inPubMed Google Scholar * Ayman H. Said View author publications You can also search for this author inPubMed Google Scholar * Bogdan M. Leu View author

publications You can also search for this author inPubMed Google Scholar * Lynn A. Boatner View author publications You can also search for this author inPubMed Google Scholar * Robert J.

McQueeney View author publications You can also search for this author inPubMed Google Scholar * Olivier Delaire View author publications You can also search for this author inPubMed Google

Scholar CONTRIBUTIONS This project included significant contributions from many researchers and all authors participated in scientific discussions. J.D.B. (experiment) and O.D. (experiment

and calculations) designed this research project. L.A.B. synthesized single-crystal samples. J.H. and O.D. performed the theoretical calculations with analysis. M.E.M., C.W.L., J.D.B., O.D.

and D.L.A. performed the INS measurements and analysis. E.D.S., J.D.B., O.D., C.W.L. and J.Z.T. performed the diffuse X-ray scattering measurements and analysis. J.D.B., M.E.M., O.D.,

C.W.L., A.H.S., B.M.L., J.Z.T. and R.J.M. performed the IXS measurements and analysis. O.D., J.D.B., M.E.M., E.D.S. and J.H. wrote the manuscript with assistance from C.W.L. CORRESPONDING

AUTHORS Correspondence to John D. Budai or Olivier Delaire. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. EXTENDED DATA FIGURES AND TABLES

EXTENDED DATA FIGURE 1 TEMPERATURE-DEPENDENT SCATTERING FUNCTION _S_(_E_). Data come from inelastic powder neutron scattering measurements integrated over _Q_ values up to ∼6 Å−1, obtained

using an incident neutron energy of 30 meV, and show gradual softening of the low-energy phonons and abrupt disappearance of these modes across the transition at temperature _T_c. EXTENDED

DATA FIGURE 2 OPTICAL PHOTOGRAPH OF RECTANGULAR VO2 SINGLE CRYSTAL MOUNTED ON COPPER POST. Crystal dimensions are 0.25 mm × 0.25 mm × ∼4 mm. Unlike larger crystals, small crystals such as

this did not show sample cracking while thermally cycling through the MIT. EXTENDED DATA FIGURE 3 INTEGRATED FIRST-ORDER TDS INTENSITY FOR A _H_ + _K_ + _L_ = 8 SHEET NEAR (4.5 0 3.5) USING

DIFFUSE X-RAY SCATTERING MEASUREMENTS FROM THE APS-33BM BEAMLINE, COMPARED WITH THE THERMAL OCCUPATION FACTOR FOR PHONONS. EXTENDED DATA FIGURE 4 IXS ENERGY SCAN. Data (filled blue circles)

are for a transverse acoustic phonon in the rutile phase measured at an M point in reciprocal space, _Q_ = (0.5, 3.5, 0), at a temperature of 810 K. The solid red line is a fit using the

expression for a damped harmonic oscillator. EXTENDED DATA FIGURE 5 IXS MEASUREMENTS FOR INDIVIDUAL PHONON BRANCHES. Schematic at left shows total scattering vectors, _Q_LA and _Q_TA, for

separate measurements of longitudinal and transverse phonons with wavevector _Q_ = (0, 0, _ζ_) (_ζ_ ≈ 0.3) along the Γ–Z symmetry direction. Plot at right shows experimental energy scan at

_Q_TA = (0, 4, 0.3) corresponding to the transverse acoustic branch. The line shape is well fitted by a strongly damped harmonic model, and the large anharmonic linewidth corresponds to a

very short phonon lifetime. EXTENDED DATA FIGURE 6 CALCULATED PHONON DISPERSIONS WITH HARMONIC APPROXIMATIONS. Data calculated at 0 K with PBE (A) and PBE+_U_ (B). Negative energies

correspond to unstable modes with imaginary frequencies which are unphysical. EXTENDED DATA FIGURE 7 DFT FROZEN-PHONON POTENTIAL ENERGY CURVES (PER ATOM). Blue curves are parabolic fits and

magenta fits include quadratic as well as quartic terms. Insets show the displacement patterns of the modes. Black dots represent DFT total energy as a function of _u_Vmax, the maximum

displacement of a V atom in the phonon mode. Vanadium and oxygen atoms are depicted by green and red, respectively. SUPPLEMENTARY INFORMATION THREE-DIMENSIONAL THERMAL DIFFUSE SCATTERING

(TDS) X-RAY MEASUREMENTS Temperature-dependent x-ray diffuse scattering measurements from VO2 single crystals were measured using an area detector as the sample was rotated. The reciprocal

lattice vector was calculated for each pixel of the detector at each angle setting. Two-dimensional and three dimensional diffuse scattering maps were calculated by averaging the counts of

all pixels contained in each voxel of a regular 0.05 x 0.05 x 0.025 rutile reciprocal-lattice grid. The Supplementary Video illustrates that, as discussed in the article, the 3-D thermal

diffuse _H_+_K_+_L_=2_n_, _n_≠0) in reciprocal space. (MOV 1675 kb) POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 POWERPOINT SLIDE FOR

FIG. 4 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Budai, J., Hong, J., Manley, M. _et al._ Metallization of vanadium dioxide driven by large phonon

entropy. _Nature_ 515, 535–539 (2014). https://doi.org/10.1038/nature13865 Download citation * Received: 13 June 2014 * Accepted: 12 September 2014 * Published: 10 November 2014 * Issue

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