Stress Response And Physical Properties Of Diamond Under Complex Strain

Diamond is one of the longest standing,best known and most influential materials in human history.Its unparalleled strength and hardness make diamond one of the earliest super materials,atop the chart of well-known superhard substances.Diamond's superior optical properties add further glare to this wonder material.Since ancient times,the outstanding characters of diamond have made it the first choice for utilization in top-notch jewelries or cutting tools.In more recent history,diamond received ever increasing attention in scientific research and technological developments.On the one hand,diamond and diamond based composites have been more systematically incorporated into cutting,grinding,and drilling tools,widely applied in industrial production,engineering operation,and precision machining;on the other hand,diamond's exceptional mechanical and optical properties have led to design and application of diamond anvil cells,which propelled high-pressure study to the forefront of modern scientific research,allowing synthesis and characterization of many novel materials at extreme pressure conditions,making this technique an essential means in modern materials research.A combination of high-pressure diamond anvil cell technique with laser-heating high-temperature conditions provides powerful and unique environments to explore mysterious states of matter that exist in distant astrophysical bodies in deep universe.The latest developments at the frontier of modern scientific exploration have further broadened the research and applications of diamond.For example,diamond with nitrogen-vacancy centers hold great promise as storage units in quantum computers,and diamond films help heat dissipation in microscale and nanoscale electronic devices,etc.In recent years,further exploration of both material and property aspects of diamond continues to attract considerable attention of the scientific community.Of particular interest are the latest development in diamond's unique material behaviors at nanoscale and novel properties under complex extreme conditions.Such cutting-edge research and development require broader assessments of structural,mechanical and electronic properties of diamond under more general loading conditions,and deeper understanding of the underlying physics mechanisms.Diamond's fundamental physical properties and characters stem from its superstrong three-dimensional carbon bonding network,highlighted by its extremely high hardness and its brittleness.The former is the most outstanding feature of diamond,while the latter its seemingly unavoidable intrinsic weakness.The discovery and production of diamond nearly coincides with human history.Over the past millennia,mining and processing have produced natural diamonds that are made in the high-temperature and high-pressure environments deep inside earth and then brought up to near Earth surface by surging crust.Since 1950's,synthetic diamond has been successfully produced,going from small-scale laboratory synthesis to large-scale industrial production and application.But it remains highly challenging to obtain high-quality,near-perfect and defect-free specimens for systematic research and exploration toward high-end applications in,for example,diamond based electromechanical devices and advanced diamond anvils for producing extreme pressure environments.The latest research indicates that,under extreme complex strain conditions diamond may exhibit extraordinary structural and stress responses.For example,recently reported synthesis of solid metallic hydrogen relied on the best diamond anvils to produce the limiting static high pressure.While the claimed discovery of solid metallic hydrogen remains controversial,the role of high-quality diamond in generating extreme pressure and its deformation at large strains attracted great attention in the scientific community.Another case in point is the recently developed double-stage diamond anvil technique,which raises new questions about diamond's behavior under complex extreme strains.All this presents great new challenges in understanding the intrinsic characters and underlying microscopic mechanisms of diamond.Following the latest developments and associated key issues raised in diamond research,combined with accumulated consideration of fundamental materials physics aspects,we have reexamined diamond in a systematic and deep exploration,which leads to a host of unexpected results.?.We find that under a large class of constrained shear strains largely unexplored in previous studies,diamond behaves qualitatively different from its well-known superior hard and brittle characteristics,and instead exhibit creeplike deformation patterns and concomitant electron conduction that usually exist only in select metallic systems in the absence of thermal effect.Diamond is well-known for its extreme stiff and brittle,and ultra wide band gap.In stark contrast to these established benchmarks,our first-principles studies unveil surprising intrinsic structural ductility and electronic conductivity in diamond under coexisting large shear and compressive strains.Analysis of associated bonding changes reveals that compression constraints could prevent cleavage-type graphitization that commonly occurs in severely strained diamond,and instead produce local bonding rearrangements via anomalously large angular variations that open new pathways for exceptional creeplike shear flow deformations.Remarkably,this structural flow process creates distinct charge-flow channels for electronic conduction,producing metallic diamond in an extended strain range.Such unusual stress responses are unprecedented in diamond or related strong covalent materials lead to surprising material and physics phenomena,including groundbreaking structural deformation mechanism and electron and hole conduction.These exceptional structural,mechanical,and electronic properties unravel extraordinary conducting phenomena in a highly ductile diamond crystal,thereby introducing the brand-new concept of “smooth flow in diamond”,which greatly expands the realm of understanding of diamond,a most famous superhard and insulating material with a long history,wide application,and extensive research record.These new findings establish a strong foundation for clarifying puzzling structural and mechanical phenomena observed in past experiments,and predicting novel material behaviors and underlying mechanisms.?.Another major discovery reported by present work is the intrinsic superconductivity in strongly deformed diamond under constrained shear strains.Previous work has reported superconductivity in boron-doped diamond.Its working principle is the coupling of boron introduced holes and the lattice vibration in diamond crystal,producing a phonon driven superconducting phenomenon.This is a charge conduction process without dissipation through externally introduced carriers.In the present work,we find a brand-new mechanism for chemical bonding change inside diamond crystal under large constrained shear strains,leading to gradual closure of the giant insulating bandgap in the original crystal and realizing an intrinsic metallic state of diamond without the need for external carrier doping and,through coupling to its own lattice vibration,generating unprecedented intrinsic superconductivity in diamond.This result has profound implications for high-pressure materials physics research.In particular,considering that during conduction or superconductivity studies metallic wires of the four-point probe for transport measurement are laid directly through the culet region of diamond anvil cell,which is most prone to metallization caused by compression constrained shear deformation.Under such circumstances,diamond's metallization would greatly impact the measurement outcome,causing short circuit,and producing false signals indicating conducting or superconducting state in the specimen.Therefore,the present work not only unveils a fundamental new superconducting phenomenon in diamond under large constrained shear strains,but also provide crucial guidance for proper design and analysis of pertinent high-pressure transport measurements.?.We report findings from first-principles calculations of stress responses to wide ranges of tensile and shear strains,creating unprecedented systematic mappings of extremal stress fields in diamond.The results unveil intriguing patterns of tensile and shear stress distributions and unexpected highly directional extremal shear stresses.The present approach introduces a protocol for characterizing crystalline solids in full strain ranges covering both elastic and plastic regimes.Here we present a systematic mapping of extremal stress fields in diamond from first-principles stress-strain calculations along many different structural deformation paths.The results reveal intriguing patterns and trends of stress responses to large-range strains in a rich variety of tensile directions and shear planes,offering a comprehensive view on peak stress distributions and associated bonding variations.In particular,we identify a surprisingly large number of easy-slip directions in many shear planes with nearly equal peak stresses compared to the established and often quoted(111)<11-2> easy-slip direction;moreover,we uncover strikingly anisotropic shear stresses with the maximal value greatly exceeding the previously known highest shear stress on record.These newly created benchmarks on extreme mechanical behaviors establish a quantitative basis for evaluating sustainable structural changes and threshold strengths at large deformations.This more comprehensive assessment approach introduces a robust protocol for characterizing essential structural and mechanical properties of crystalline solids in full ranges of deformation modes,which are crucial to elucidating material behaviors and guiding rational performance optimization.