arXiv subjects

John B. Parise

Publications and source records attributed to John B. Parise.

5 recordsLinked to original sources

arXiv2026

Exotic centrosymmetric phase of acentric urea under high pressure

Urea is a simple prototype supramolecular crystal that exhibits rich polymorphism at low pressure due to broken and restored N-H-O hydrogen bonds. The high pressure polymorph (phase V') of acentric urea crystallizes in a centrosymmetric structure, which presents an appealing target because of its potential exotic structure, analogous to the symmetric ice phase X. The pressure-induced polymorphism of urea was studied using powder X-ray diffraction, infrared and Raman spectroscopy, second harmonic generation (SHG) measurements up to 20 GPa and ab initio crystal structure prediction (CSP) based on the constrained evolutionary approach. A strong decrease of the SHG signal at the transition pressure 10 GPa reveals that the high-pressure polymorph is indeed centrosymmetric, further confirmed by the selection rules observed in the lattice vibration modes, in contrast to chemical intuition for acentric urea. The structural evolution sequence obtained from X-ray diffraction, SHG and CSP calculations is as follows: phase I (P421m; Z=2) from 0 to 0.5 GPa, Phase III (P212121; Z=4) from 0.5 to 5.2 GPa, and phase V' (P21/m; Z=6) beyond 10.0 GPa which is energetically competitive with the theoretically predicted phase V (Pnma; Z=4). A phase X with distinct spectral and diffraction features forms between 5.2 and 10.0 GPa, which could be explained by a quantum disorder intermediate state between phase III and V', that is ascribed to the difficulty to disrupt the H-bonding network under extremely compressed environment. The softening of N-H vibrations and the change in intensity of the vibrations associated with the hydrogen bonding provide evidence for proton tunneling and charge-transfer interaction in phase X.

cond-mat.mtrl-sci↗

arXiv2022

Lattice Instability and Ultralow Lattice Thermal Conductivity of Layered PbIF

Understanding the interplay between various design strategies (for instance, bonding heterogeneity and lone pair induced anharmonicity) to achieve ultralow lattice thermal conductivity ($κ_l$) is indispensable for discovering novel functional materials for thermal energy applications. In the present study, we investigate layered PbXF (X = Cl, Br, I), which offers bonding heterogeneity through the layered crystal structure, anharmonicity through the Pb$^{2+}$ $6s^2$ lone pair, and phonon softening through the mass difference between F and Pb/X. The weak inter-layer van der Waals bonding and the strong intra-layer ionic bonding with partial covalent bonding result in a significant bonding heterogeneity and a poor phonon transport in the out-of-plane direction. Large average Grüneisen parameters ($\geq$ 2.5) demonstrate strong anharmonicity. The computed phonon dispersions show flat bands, which suggest short phonon lifetimes, especially for PbIF. Enhanced Born effective charges are due to cross-band-gap hybridization. PbIF shows lattice instability at a small volume expansion of 0.1$\%$. The $κ_l$ values obtained by the two channel transport model are 20-50$\%$ higher than those obtained by solving the Boltzmann transport equation. Overall, ultralow $κ_l$ values are found at 300 K, especially for PbIF. We propose that the interplay of bonding heterogeneity, lone pair induced anharmonicity, and constituent elements with high mass difference aids the design of low $κ_l$ materials for thermal energy applications.

cond-mat.mtrl-sci↗

arXiv2022

Lattice instability, anharmonicity and Raman spectra of BaO under high pressure: A first principles study

Alkaline-earth metal oxides, in particular MgO and CaO dominate Earths lower mantle, therefore, exploring high pressure behavior of this class of compounds is of significant geophysical research interest. Among all these compounds, BaO exhibits rich polymorphism in the pressure range of 0-1.5 Mbar. Static enthalpy calculations revealed that BaO undergoes a pressure induced structural phase transition from NaCl-type (B1) $\rightarrow$ NiAs-type (B8) $\rightarrow$ distorted CsCl-type (d-B2) $\rightarrow$ CsCl-type (B2) at 5.1, 19.5, 120 GPa respectively. B1 $\rightarrow$ B8 $\&$ B8 $\rightarrow$ d-B2 transitions are found to be first order in nature whereas d-B2$\rightarrow$ B2 is a second order or weak first order phase transition. Interestingly, d-B2 phase shows stability over a wide pressure range, $\sim$19.5-113 GPa. Mechanical and dynamical stabilities of ambient and high pressure phases are demonstrated through computed elastic constants and phonon dispersion curves, respectively. Under high pressure, significant phonon softening and soft phonon mode along M-direction are observed for B8, d-B2 and B2 phases, respectively. Pressure dependent Raman spectra suggest a phase transition from d-B2 to Raman inactive phase under pressure. Overall, the present study provides a comprehensive understanding of underlying mechanisms behind pressure-induced structural phase transitions in BaO.

cond-mat.mtrl-sci↗

arXiv2021

Anomalous Lattice Thermal Conductivity in Rocksalt IIA-VIA Compounds

Materials with an intrinsic (ultra)low lattice thermal conductivity (k$_L$) are critically important for the development of efficient energy conversion devices. In the present work, we have investigated microscopic origins of low k$_L$ behavior in BaO, BaS and MgTe by exploring lattice dynamics and phonon transport of 16 iso-structural MX (Mg, Ca, Sr, Ba and X = O, S, Se and Te) compounds in the rocksalt (NaCl)-type structure by comparing their lattice transport properties with the champion thermoeletric iso-structural material, PbTe. Anomalous trends are observed for k$_L$ in MX compounds except the MgX series in contrast to the expected trend from their atomic mass. The underlying mechanisms for such low k$_L$ behavior in relatively low atomic mass systems namely BaO, BaS and MgTe compounds are thoroughly analyzed. We propose the following dominant factors that might be responsible for low k$_L$ behavior in these materials: 1) softening of transverse acoustic (TA) phonon modes despite low atomic mass, 2) low lying optic (LLO) phonon modes fall deep into acoustic mode region which enhances overlap between longitudinal acoustic (LA) and LLO phonon modes which increases scattering phase space, 3) short phonon lifetimes and high scattering rates, 4) relatively high density (\r{ho}) and large Grüneisen parameter. Moreover, tensile strain also causes a further reduction in k$_L$ for BaO, BaS and MgTe through phonon softening and near ferroelectric instability. Our comprehensive study on 16 binary MX compounds might provide a pathway for designing (ultra)low k$_L$ materials even with simple crystal systems through phonon engineering.

cond-mat.mtrl-sci↗

arXiv2020

Origin of superconductivity and giant phonon softening in TlInTe$_2$ under pressure

Analogous to 2D layered transition metal dichalcogenides, the TlSe family of 1D chain materials with Zintl-type structure exhibits exotic phenomena under high-pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe 2 using Raman spectroscopy, synchrotron X-ray diffraction, and transport measurements, in combination with crystal structure prediction (CSP) based on the evolutionary approach and first principles calculations. We found that TlInTe$_2$ undergoes a pressure driven semiconductor to semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with Tc = 3.8 K) induced by a Lifshitz transition. The Lifshitz transition is initiated by the appearance of new electron pockets on the Fermi surface, which evolve with pressure and connect to the adjacent electron pockets forming an umbrella shaped Fermi surface at the top and bottom of the Brillouin zone. An unusual giant phonon softening (Ag mode) concomitant with a V-shaped Tc behavior appears at 10-12 GPa as a result of the interaction of optical phonons with the conduction electrons, resulting in Fano line shaped asymmetry in Ag mode. A prominent Tc anomaly concurrent with the Ag mode softening at 19-20 GPa is correlated to the semimetal to metal transition. The CSP calculations reveal that these transitions are not accompanied by any structural phase transitions up to the maximum pressure achieved, 33.5 GPa. Our findings on TlInTe$_2$ open up a new platform to study a plethora of unexplored high pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), phonon softening and electron-phonon coupling.

cond-mat.supr-con↗