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Spherical crystals in minerals from prismatine-bearing rock from Waldheim, including ultrahigh-pressure (UHP) minerals such as stishovite and coesite, were previously described in uncommon crustal environments. To determine if this was an outlier phenomenon, we searched for equivalent inclusions in other rocks, which we indeed discovered in a Variscan tin-bearing granite sensu stricto from the Erzgebirge/Germany. The identification of more examples of this phenomenon implies a novel, very rapid transcrustal transport mechanism, which, however, is not unique. We demonstrate the unusual occurrence of UHP minerals (moissanite, diamond, lonsdaleite, stishovite, coesite, kumdykolite, and cristobalite-II) in topaz the investigated granitic samples, which reflects the direct interaction of mantle and crust via supercritical fluids or extremely volatile-rich melts. Mostly, the UHP minerals we recognized occur as tiny inclusions in moissanite. The trapping by this mineral prevents a fast reaction in an exogenous environment.

We present ab initio calculations of the electronic and optical properties of hexagonal SiGe alloys in the lonsdaleite structure. Lattice constants and electronic band structures in excellent agreement with experiment are obtained using density-functional theory. Hexagonal Si has an indirect band gap, while hexagonal Ge has a pseudo-direct gap, i.e. the optical transitions at the minimum direct band gap are very weak. The pseudo-direct character of pure hexagonal Ge is efficiently lifted by alloying. Already for a small admixture of Si, symmetry reduction enhances the oscillator strength of the lowest direct optical transitions. The band gap is direct for a Si content below 45 %. We validate lonsdaleite group-IV alloys to be efficient optical emitters, suitable for integrated optoelectronic applications.

In this report, a new carbon allotrope named nanoleite is proposed. Its crystal structure is constructed by embedding carbon nanotubes into the matrix of lonsdaleite periodically, leading to a hexagonal primitive unit cell. The equilibrium structure of nanoleite is fully relaxed by density functional theory calculation, and we demonstrate that nanoleite is a semiconductor with an indirect energy bandgap of 2.06 eV. Furthermore, it has a high absorption coefficient in the visible spectrum range, which is comparable to that of the gallium arsenide and indium phosphide. X-ray diffraction patterns and phonon modes are also studied.

Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were characterized with a range of techniques. Using the MCDIFFaX approach for analysing X-ray diffraction data, hexagonality indices up to 40% were found. The effects of increasing amounts of hexagonal stacking on the Raman spectra of diamond were investigated computationally and found to be in excellent agreement with trends in the experimental spectra. Electron microscopy revealed nanoscale twinning within the cubic diamond structure. Our analyses lead us to propose a systematic protocol for assigning specific hexagonality attributes to the mineral designated as lonsdaleite among natural and synthetic samples.

Bicontinuous membranes in cell organelles epitomise nature’s ability to create complex functional nanostructures. Like their synthetic counterparts, these membranes are characterised by continuous membrane sheets draped onto topologically complex saddle-shaped surfaces with a periodic network-like structure. In cell organelles, their structure sizes around 50–500 nm and fluid nature make Transmission Electron Microscopy (TEM) the analysis method of choice to decipher nanostructural features. Here we present a tool to identify bicontinuous structures from TEM sections by comparison to mathematical “nodal surface” models, including the hexagonal lonsdaleite geometry. Our approach, following pioneering work by Deng and Mieczkowski (1998), creates synthetic TEM images of known bicontinuous geometries for interactive structure identification. We apply the method to the inner membrane network in plant cell chloroplast precursors and achieve a robust identification of the bicontinuous diamond surface as the dominant geometry in several plant species. This represents an important step in understanding their as yet elusive structure-function relationship.

We explore the structural evolution of highly oriented pyrolytic graphite (HOPG) under detonation-induced shock conditions using in situ synchrotron x-ray diffraction in the ns timescale. We observe the formation of hexagonal diamond (lonsdaleite) at pressures above 50 GPa, in qualitative agreement with recent gas gun experiments. First-principles density functional calculations reveal that under uniaxial compression, the energy barrier for the transition toward hexagonal diamond is lower than that for cubic diamond. Finally, no indication of cubic diamond formation was observed up to $g70$ GPa.

We report the results of a study of the polycrystalline powder of the diamond-lonsdaleite from the Popigai crater (Siberia) using UV micro-Raman spectroscopy and high-resolution synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond-lonsdaleite samples with close amounts of diamond and lonsdaleite, we were able to identify the polytypic composition of impact diamonds in contrast to the method of X-ray diffraction. We have managed to get for the first time the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all the three Raman - active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.

The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from layered and bonded sp3 and sp2 nanostructural units and provide a framework for classifying the members of this new class of materials. The nanocomposite structures are identified within both natural impact diamonds and laboratory-shocked samples and possess diffraction features that have previously been assigned to lonsdaleite and postgraphite phases. The diaphite nanocomposites represent a new class of high-performance carbon materials that are predicted to combine the superhard qualities of diamond with high fracture toughness and ductility enabled by the graphitic units and the atomically defined interfaces between the sp3- and sp2-bonded nanodomains.

For the first time, 60 large diamond aggregates were found inside the Popigai meteorite crater during washing of alluvial deposits along the Dogoi river crossing the crater. These aggregates are similar in appearance to yakutites from the placers of Northern Yakutia (YPY), and we regard them as yakutites from the Popigai crater (YPC). The structure and optical properties of Popigai impact diamonds from the impact melt rocks (tagamites) in the crater (PIDT) and yakutites YPC/YPY were compared in detail. In all these cases, a polycrystalline structure consisting of nanoscale grains of cubic and twinned cubic diamond (lonsdaleite) was found. This is the result of a solid-phase graphite-diamond transition due to an impact event 35 million years ago. The diamond aggregates show the following features: a red shift of the short-wave edge of the transmission, broadening of the diamond Raman peaks, signals from other diamond polytypes and numerous inclusions of other minerals in the Raman spectra, and a dominant broadband photoluminescence (PL). PL in the N3 system associated with N3V centers in PIDT diamonds indicates a high-temperature annealing of these aggregates with resulting aggregation of impurities during the prolonged cooling of large impact melt pockets and pools. It is assumed that some of the impact diamonds were ejected from the crater during the impact event and experienced rapid cooling. Some of these diamonds fell back into the crater (YPC yakutites), others have been deposited outside the crater and displaced during erosion (YPY yakutites). Difference in size and shape between the PIDTs and yakutites YPC/YPY is due to the difference in size of original graphite flakes or aggregates and/or due to the fundamentally different technologies of diamond extraction.

International audience; The purpose of this paper is to predict the existence of novel 3D covalent ultra-hard carbon allotropes in view of synthesizing them eventually. Stability and spectroscopic characteristics of the rarely occurring tricarbon linear molecule from quantum chemistry calculations are extended to the solid state based on crystal chemistry considerations and quantum density functional theory ground state calculations letting devise rhombohedral rh-C3 (h-C9) and hexagonal h-C6 proposed as ultra-hard carbon allotropes like lonsdaleite. Two crystallographic different carbons forming linear C2-C1-C2 unit are characterized as sp3-like C2 with an angle of 106.17° smaller than ideal 109.4°, and sp1 C1. The calculated elastic constants are positive and their combinations obey the required stability criteria; furthermore they point to a strong anisotropy of the mechanical properties of the two allotropes rh-C3 (h-C9) and h-C6 with exceptionally large C33 values (1636 GPa and 1610 GPa, respectively), exceeding that of lonsdaleite (1380 GPa). The phonon dispersion curves stress furthermore the dynamical stability of the two carbon allotropes by showing positive frequencies throughout the hexagonal Brillouin zone. A significant separation between the highest frequencies of the optic modes illustrates the rigidity of the bonding within linear C3 building block and the whole structure. Both allotropes are characterized by large bulk moduli and high hardness values that are only slightly less than those of lonsdaleite and diamond. Weak metallic behavior of both new carbon allotropes were identified from electronic band structure calculations and explained by the mixed sp1-sp3 hybridizations, likewise other carbon allotropes from literature: m-C12 (sp1-sp2) and h-C18 (sp2-sp3).

The stacking sequence significantly affects the thermal conductivity of diamond. However, the inaccuracy of some widely used empirical potentials to calculate the anharmonic phonon transport in diamond, hinders the use of molecular dynamics simulations from revealing the detailed mechanism of phonon transport in diamond and other related materials with different stacking sequences. In this paper, a comparative study of four common carbon empirical potentials - Tersoff, Airebo, 2nd-rebo, and COMPASS - is performed to simulate the phonon thermal transport of diamond and lonsdaleite. The results show that the Tersoff potential, together with Airebo and 2nd-rebo potentials, is not suitable for describing the phonon transport mechanism in different diamond polytypes, both for harmonic phonon dispersion and anharmonic phonon scattering caused by stacking disorders. COMPASS potential gives a good fit for the acoustic phonon branches in all directions of diamond and accurately describes the band gaps between acoustic and optical branches, and is capable of representing the lattice dynamics and phonon thermal transport in diamond and lonsdaleite. The COMPASS potential is suitable for simulating the phonon thermal transport properties in diamond and lonsdaleite, and thus it is suitable for simulating the stacking disorder effect on the phonon thermal transport in diamond.

The structural, mechanical and electronic properties of carbon allotropes were systematically investigated by the first-principles calculations in this study, and the origin of high hardness of carbon allotropes was analyzed. We studied the mechanical properties, including the elastic moduli, Poisson’s ratio and Vickers hardness, of six novel carbon allotropes and compared with two known superhard carbon phases (diamond and lonsdaleite). It was found that six novel carbon allotropes exhibit the potential to be superhard materials. Besides, the band structures and electronic density of states of these carbon allotropes were calculated as well, and the superhard properties of the six novel carbon allotypes were preliminarily revealed. Finally, the tiling approach was adopted to analyze the origin of high hardness of six novel carbon allotropes from the perspective of structure.

International audience; A new ultra-hard rhombohedral carbon rh-C4 (or hexagonal h-C12) is reported as derived from 3R graphite through crystal chemistry construction and ground state energy within the density functional theory. A resulting cohesive extended hexagonal three-dimensional network of h-C12 is identified as formed of C4 tetrahedra like in cubic and hexagonal diamond. The electronic band structure of rh-C4 is characteristic of insulator with Egap ​= ​4 ​eV similarly to diamond. From the energy-volume equations of state and the set of elastic constants a larger value of bulk modulus versus lonsdaleite, and the largest Vickers hardness (Hv) versus both forms of diamond were revealed. The phonon band structure showing only real wave numbers further confirms the stability of the new carbon phase.

The structural, elastic, elastic anisotropic, thermodynamic and electronic properties of Lonsdaleite C, Si and Ge and Lonsdaleite C–Si and Si–Ge alloys are investigated using density functional theory. The elastic anisotropy calculations show that the Lonsdaleite C0.25Si0.75 alloy has the greatest anisotropy in Poisson’s ratio, shear modulus, bulk modulus and Young’s modulus. Through the mixing of carbon and silicon and silicon and germanium at certain proportions, Lonsdaleite C0.25Si0.75 with metallic properties and Lonsdaleite Si0.25Ge0.75 with a direct band gap are obtained, where Lonsdaleite Si0.25Ge0.75 is a narrow direct band gap semiconductor with a band gap of 0.76 eV at the HSE06 hybrid functional level. The minimum thermal conductivity calculations on Lonsdaleite C–Si and Si–Ge alloys show that the minimum thermal conductivities of Lonsdaleite C0.75Si0.25 and Lonsdaleite C0.5Si0.5 are greater than that of diamond C, and the minimum thermal conductivities of Lonsdaleite C–Si and Si–Ge alloys in different directions are also investigated.

This paper describes the problem of the behavior of a mixture of small graphite particles with water in the conditions of shock-wave action at a pressure of 32 GPa and a temperature of up to 1200–1600 K. Graphite particles at these pressures and temperatures are capable of transforming into cubic diamonds or at least into their hexagonal form that is lonsdaleite. It is shown that, for sufficiently small graphite particles of the order of 1 μm, their mixture with water for about 10 μs can heat up to the above-mentioned temperatures and undergo phase transformation, remain in those conditions for about 50 μs, and then efficiently cool down during the next 50 μs to the temperatures below 300 K, while remaining in the diamond phase.

We introduce a computational approach to estimate the hardness and stiffness of diamond surfaces and nanoparticles by studying their elastic response to atomic nanoindentation. Results of our ab initio density functional calculations explain the observed hardness differences between different diamond surfaces and suggest bond stiffening in bare and hydrogenated fragments of cubic diamond and lonsdaleite. The increase in hardness and stiffness can be traced back to bond length reduction especially in bare nanoscale diamond clusters, a result of compression that is driven by the dominant role of the surface tension., Comment: 7 pages, 3 figures

The electronic structure and dielectric properties of the diamond, body centered cubic diamond (bc8), and hexagonal diamond (lonsdaleite) phases of carbon are computed using density functional theory and many-body perturbation theory with the emphasis on the excitonic picture of the solid phases relevant in the regimes of high-pressure physics and warm dense matter. We also discuss the capabilities of reproducing the inelastic x-ray scattering spectra in comparison with the existing models in light of recent x-ray scattering experiments on carbon and carbon bearing materials in the Megabar range., 25 pages, 25 figures

We propose a new class of carbon allotropes obtained by combining linear sp carbon chains with sp3 bulk carbon.The structure of these crystalline carbon allotropes consists of sp chains inserted in cylindrical cavities periodically arranged in hexagonal diamond (lonsdaleite).We carry out a detailed computational analysis of the structural, electronic, and vibrational properties of a simple form in this class: a single C6 strand embedded in a nm-sized cavity.We obtain a metallic allotrope exhibiting characteristic high-frequency vibrations associated with the sp chains stretching modes, and characterized by long-time room-temperature stability.In addition, we suggest how numerous similar allotropes could be constructed within this class, that we call zayedene, all characterized by comparable metallicity and high-frequency vibrations.

The concentration of diamond-bearing tagamite from the Popigai impact crater produces large amounts of graphite in addition to impact diamonds (1:100, respectively). The question arises of whether this is residual graphite not converted to diamond at the time of the Popigai impact or is a retrograde form resulting from back-conversion of impact diamond to graphite in a high-temperature tagamite melt. Experiments show that graphite from tagamite is a residual phase. Coexistence of lonsdaleite, cubic diamond, and single-crystal graphite within a limited volume may be due to different orientations of the graphite base plane relative to the impact stress direction. Thus, the diamond-bearing rocks may contain significant amounts of residual graphite, which is consistent with published evidence.

International audience; Nanosized and crystalline sp3-bonded carbon materials were prepared over large surface areas up to ∼33 × 51 μm2 from the exposure of few-layer graphene (FLG) to H radicals produced by the hot-filament process at low temperature (below 325 °C) and pressure (50 Torr). Hybrid materials were also obtained from the partial conversion of FLG. sp3-C related peaks from diamond and/or lonsdaleite and/or hybrids of both were detected in UV and visible Raman spectra. CH bonding was directly detected by Fourier Transform Infrared (FTIR) microscopy over an area of ∼150 μm2 and one single component attributed to sp3-CH mode was detected in the CH stretching band showing that carbon is bonded to one single hydrogen and strongly suggesting that the sp3-C materials obtained are ultrathin films with basal planes hydrogenated. The experimental results are compared to computational predictions and comprehensively discussed. Those materials constitute new synthetic carbon nanoforms after fullerenes, nanodiamonds, carbon nanotubes and graphene. This opens the door to new research in multiple areas for the development of new potential applications and may have wide scientific impact, including for the understanding of extraterrestrial diamond-related structures and polytype formation mechanism(s).

Although diamond is the hardest material, it would still be deformed by indenting. Therefore, investigating its incipient plasticity during the indenting process should be of great interest. Through molecular dynamics simulations, we have investigated the nanoindentations of diamond and probed its incipient plasticity according to the obtained load–displacement (P–h) curve. We found that the incipient plasticity of diamond should result from the propagation of the dislocations and the structural phase transitions from cubic diamond to lonsdaleite. The probable physical processes of incipient plasticity of diamond during nanoindentation were also suggested. The results presented in this work would not only provide clues for detecting the pop-in event of diamond in the future experimental work, but also offer new insights into the plasticity of diamond, which could be beneficial to the design of novel nano-structured superhard materials and elucidating the origins of wear and friction.

The possible presence of the high-density carbon polymorph with hexagonal symmetry known as "lonsdaleite" provides an important marker for shock impact events. It is typically considered to form as a metastable phase produced from graphite or other carbonaceous precursors. However, its existence has recently been called into question. Here we collected high-resolution synchrotron X-ray diffraction data for laboratory-shocked and natural impact diamonds that both show evidence for deviations from cubic symmetry, that would be consistent with the appearance of hexagonal stacking sequences. These results show that hexagonality can be achieved by shocking diamond as well as from graphite precursors. The diffraction results are analyzed in terms of a general model that describes intermediate stacking sequences between pure diamond (fully cubic) and "lonsdaleite" (fully hexagonal) phases, with provision made for ordered . vs disordered stacking arrangements. This approach provides a "hexagonality index" that can be used to characterize and distinguish among samples that have experienced different degrees of shock or static high pressure-high temperature treatments. We have also examined the relative energetics of diamond and "lonsdaleite" structures using density functional theoretical (DFT) methods. The results set limits on the conditions under which a transformation between diamond and "lonsdaleite" structures can be achieved. Calculated Raman spectra provide an indicator for the presence of extended hexagonal stacking sequences within natural and laboratory-prepared samples. Our results show that comparable crystallographic structures may be developed by impact-generated shockwaves starting from ambient conditions using either of the two different allotropes of carbon (diamond, graphite). This broadens the scope for its occurrence in terrestrial and planetary systems.

High-resolution transmission electron microscopy (HRTEM) studies of silicon after treatment in a planetary mill have been performed. It is shown that along with the initial phase of silicon, Si-I, the sample also contains some high-pressure phases: Si-III (Kasper phase) and Si-IV (lonsdaleite). We studied the orientation relationship between the particles of different phases, finding that there are, in general, two mechanisms of formation of Si-IV: (1) through the stacking faults formation; (2) through the transformation first to the Kasper phase (Si-III), and then from the Kasper phase to Si-IV. Estimations of temperature and pressure conditions in the planetary ball mill made previously are in accordance with the conditions of formation of the above-mentioned phases.

A new family of three-dimensional hydrocarbon polymers which are more energetically favorable than benzene is proposed. Although structurally these polymers are closely related to well known diamond and lonsdaleite carbon structures, using topological arguments we demonstrate that they have no known structural analogs. Topological considerations also give some indication of possible methods of synthesis. Taking into account their exceptional optical, structural and mechanical properties these polymers might have interesting applications.

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites., Shock synthesis of diamond and even harder carbon polymorphs from graphite is of great interest for science and technology. Here, the authors present unprecedented in situ measurements of the structural changes, showing ultrafast formation of diamond and, at higher pressures, evidence for a pure lonsdaleite structure.

Division and classification of abrasives development periods is discussed. Abrasives of natural origin and hard and super hard synthetic abrasive currently used in the industry, are presented. The prospects of the appearance of ultra-hard abrasives in the form of hexagonal lonsdaleite and metallic hydrogen, are indicated.

Diamond is an attractive material due to its extreme hardness, high thermal conductivity, quantum optical, and biomedical applications. There is still much that is not understood about how diamonds form, particularly at room temperature and without catalysts. In this work, a new route for the formation of nanocrystalline diamond and the diamond-like phase lonsdaleite is presented. Both diamond phases are found to form together within bands with a core-shell structure following the high pressure treatment of a glassy carbon precursor at room temperature. The crystallographic arrangements of the diamond phases revealed that shear is the driving force for their formation and growth. This study gives new understanding of how shear can lead to crystallization in materials and helps elucidate how diamonds can form on Earth, in meteorite impacts and on other planets. Finally, the new shear induced formation mechanism works at room temperature, a key finding that may enable diamond and other technically important nanomaterials to be synthesized more readily.

Nearly 2D diamond, or diamane, is coveted as an ultrathin sp3 -carbon film with unique mechanics and electro-optics. The very thinness (≈h) makes it possible for the surface chemistry, for example, adsorbed atoms, to shift the bulk phase thermodynamics in favor of diamond, from multilayer graphene. Thermodynamic theory coupled with atomistic first principles computations predicts not only the reduction of required pressure (p/p∞ > 1 - h0 /h) but also the nucleation barriers, definitive for the kinetic feasibility of diamane formation. Moreover, the optimal adsorbent chair-pattern on a bilayer graphene results in a cubic diamond lattice, while for thicker precursors the adsorbent boat-structure tends to produce hexagonal diamond (lonsdaleite), if graphene is in AA' stacking to start with. As adsorbents, H and F are conducive to diamond formation, while Cl appears sterically hindered.

Popigai is the world largest crater produced by an impact event. Abundant graphite in the target rocks underwent martensitic transformation into a mixture of high-pressure phases (an aggregate of nanometer cubic diamond and hexagonal lonsdaleite crystals), and some amount of graphite survived as a residual phase. They are of two types: (i) diamonds extracted from tagamites as chips of grains crushed during processing; (ii) yakutites in placers inside and around the crater, which formed at the impact epicenter and dispersed during the event. The impact diamonds possess exceptional abrasive strength, 1.8 to 2.4 times greater than in synthetic diamonds. The outstanding wear resistance, a large specific surface area and a thermal stability (200–250 °C greater than in synthetic diamonds) are favorable for main technological uses. With these properties, impact diamonds are valuable as material for composites and tools.

The computational prediction of superhard materials would enable the in silico design of compounds that could be used in a wide variety of technological applications. Herein, good agreement was found between experimental Vickers hardnesses, Hv, of a wide range of materials and those calculated by three macroscopic hardness models that employ the shear and/or bulk moduli obtained from: (i) first principles via AFLOW-AEL (AFLOW Automatic Elastic Library), and (ii) a machine learning (ML) model trained on materials within the AFLOW repository. Because $$H_{\mathrm{v}}^{{\mathrm{ML}}}$$ H v ML values can be quickly estimated, they can be used in conjunction with an evolutionary search to predict stable, superhard materials. This methodology is implemented in the XtalOpt evolutionary algorithm. Each crystal is minimized to the nearest local minimum, and its Vickers hardness is computed via a linear relationship with the shear modulus discovered by Teter. Both the energy/enthalpy and $$H_{{\mathrm{v,Teter}}}^{{\mathrm{ML}}}$$ H v,Teter ML are employed to determine a structure’s fitness. This implementation is applied towards the carbon system, and 43 new superhard phases are found. A topological analysis reveals that phases estimated to be slightly harder than diamond contain a substantial fraction of diamond and/or lonsdaleite.

We combine state-of-the-art Green's-function methods and nonequilibrium molecular dynamics calculations to study phonon transport across the unconventional interfaces that make up crystal-phase and twinning superlattices in nanowires. We focus on two of their most paradigmatic building blocks: cubic (diamond/zinc blende) and hexagonal (lonsdaleite/wurtzite) polytypes of the same group-IV or III–V material. Specifically, we consider InP, GaP and Si, and both the twin boundaries between rotated cubic segments and the crystal-phase boundaries between different phases. We reveal the atomic-scale mechanisms that give rise to phonon scattering in these interfaces, quantify their thermal boundary resistance and illustrate the failure of common phenomenological models in predicting those features. In particular, we show that twin boundaries have a small but finite interface thermal resistance that can only be understood in terms of a fully atomistic picture., We acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) under grants FEDER-MAT2017-90024-P, TEC2015-67462-C2-1-R (MINECO/FEDER) and RTI2018-097876-B-C21 (MICINN/FEDER), the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and by the Generalitat de Catalunya under grants no. 2014 SGR 301 and 2017 SGR 1506. M. L. S. is funded through a Juan de la Cierva fellowship. M. R. M. acknowledges support from FPU2016/02565., We acknowledge support of the publication fee by the CSIC Open Access Support Initiative through its Unit of Information Resources for Research (URICI)