Disorder and long-range interactions are two of the key components that make material failure an interesting playfield for the application of statistical mechanics. The cornerstone in this respect has been lattice models of the fracture in which a network of elastic beams, bonds, or electrical fuses with random failure thresholds are subject to an increasing external load. These models describe on a qualitative level the failure processes of real, brittle, or quasi-brittle materials. This has been particularly important in solving the classical engineering problems of material strength: the size dependence of maximum stress and its sample-to-sample statistical fluctuations. At the same time, lattice models pose many new fundamental questions in statistical physics, such as the relation between fracture and phase transitions. Experimental results point out to the existence of an intriguing crackling noise in the acoustic emission and of self-affine fractals in the crack surface morphology. Recent advances ...

Statistical models of fracture

Isostructural ZrW2O8 and HfW2O8 show strong negative thermal expansion from 0.3 K up to their decomposition temperatures of approximately 1050 K. This behavior is especially unusual because these compounds are apparently cubic over their entire existence range. Detailed structural studies of ZrW2O8 were conducted using high-resolution neutron powder diffraction data taken at 14 temperatures from 0.3 to 693 K. Below 428 K, ZrW2O8 adopts the acentric space group P213 and has a well-ordered structure containing corner-sharing ZrO6 octahedra and two crystallographically distinct WO4 tetrahedra. Above the phase transition at 428 K, which appears to be second order, the space group becomes centric Pa3. The structure is now disordered with one oxygen site 50% occupied, suggesting the possibility of high oxygen mobility. Oxygen motion above 428 K is also suggested by dielectric and ac impedance measurements. The negative thermal expansion of ZrW2O8 and HfW2O8 is related to transverse thermal vibrations of bridgi...

Negative Thermal Expansion in ZrW2O8 and HfW2O8

A new fabrication method to produce homogeneously fluorescent nanodiamonds with high yields is described. The powder obtained by high energy ball milling of fluorescent high pressure, high temperature diamond microcrystals was converted in a pure concentrated aqueous colloidal dispersion of highly crystalline ultrasmall nanoparticles with a mean size less than or equal to 10 nm. The whole fabrication yield of colloidal quasi-spherical nanodiamonds was several orders of magnitude higher than those previously reported starting from microdiamonds. The results open up avenues for the industrial cost-effective production of fluorescent nanodiamonds with well-controlled properties.

https://iopscience.iop.org/article/10.1088/0957-4484/20/23/235602/pdf

High yield fabrication of fluorescent nanodiamonds

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy () centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K?350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubits in the ground states and propose methods to extend coherence times of qubits.

/pdf/electron-phonon-processes-of-the-silicon-vacancy-centre-in-1j3saq5jf1.pdf

Electron–phonon processes of the silicon-vacancy centre in diamond

Using deftly designed and fabricated devices combining nitrogen-vacancy centers with on-chip heating and thermometry components, a group at University of California, Santa Barbara, expand the measurement, understanding, and control of single spins in the NV centers into a broad thermal range spanning from room temperature to above 600 K.

https://link.aps.org/pdf/10.1103/PhysRevX.2.031001

Measurement and Control of Single Nitrogen-Vacancy Center Spins above 600 K

Measurements of lattice parameters were made for a single crystal of a high-purity synthetic diamond using the x-ray-diffraction Bond method between 4.2 and 300 K. The key features of the present measurement are as follows: (1) The lattice parameter is determined with an accuracy of ${10}^{\ensuremath{-}6}.$ (2) A very small negative thermal expansion is detected between 30 and 90 K. (3) Thermal expansion shows a behavior of the ${T}^{4}$ law represented by the Debye theory within the measuring temperature range. By comparing the present results with the previously reported results for nitrogen-doped diamond and boron-doped diamond, it is found that diamond becomes harder following doping by nitrogen.

Thermal expansion of a high purity synthetic diamond single crystal at low temperatures

We report electrical transport measurements of synthetic diamonds doped with boron about 100 ppm. The resistivity has been measured in the temperature range 20--300 K by the van der Pauw method. We have also investigated infrared absorption coefficient at room temperature. Furthermore, we have studied the effect of ${\mathrm{P}}^{+9}$ ion irradiations with 150 MeV which introduce donor defects and also the influence of the annealing after the irradiation. The key features of the present measurement are as follows: (i) The observed temperature dependence of resistivity shows characteristic features of the variable-range-hopping (VRH). A crossover from ${T}^{\ensuremath{-}1/4}$ behavior of Mott VRH to the ${T}^{\ensuremath{-}1/2}$ form of Efros VRH is found to occur at 100 K. (ii) Below 50 K we have observed the hard gap ${T}^{\ensuremath{-}1}$ form. The width of the hard gap is about 10 meV. (iii) The experimental results are quantitatively explained by the theory of VRH. (iv) The observed width of the optical hard gap is equal to that of the hard gap obtained from resistivity. (v) The annealing effects appear only in the hard gap region and do not appear in the variable-range-hopping region. This result leads to the speculation that the hard gap is weakened by the lattice defects.

Transport of heavily boron-doped synthetic semiconductor diamond in the hopping regime

The lattice parameter of synthetic diamond single crystals has been measured in the range 4.2-320 K by the X-ray diffraction method. The lattice parameter is found to be nearly constant between 4.2 and 90 K. The thermal expansion coefficient α calculated from the experimental results is very small (of the order of 10-7 or less) and no definite evidence of the negative thermal expansion is found within our relative experimental accuracy of the order of ±1×10-6.

https://iopscience.iop.org/article/10.1143/JJAP.31.2527/pdf

Thermal Expansion Coefficient of Synthetic Diamond Single Crystal at Low Temperatures

The lattice parameter of a single-crystal boron-doped synthetic diamond has been measured in the range 4.2-300 K by x-ray diffraction (Bond method), with precision . Over the whole range the results are consistent with A, where T is the absolute temperature. The dilation due to doping indicates a boron concentration of about 100 ppm. The increase of thermal expansion over that of an undoped synthetic diamond is found to be unexpectedly large (10-15%), giving an apparent dilation on doping that is markedly temperature dependent.

http://iopscience.iop.org/article/10.1088/0953-8984/10/6/010/pdf

Thermal expansion of a boron-doped diamond single crystal at low temperatures

The thermal expansion of the lattice constant of InP crystal has been measured in the range 4.2-300 K by the Bond method and the results are shown graphically. The thermal expansion coefficient alpha calculated from the experimental results is negative between 15 and 80 K and positive below 15 K. The corresponding Gruneisen parameter gamma closely follows the behaviour of alpha and the values of alpha and gamma are tabulated and shown graphically. The results do not agree with the phenomenological theory in which only a negative alpha is predicted for InP at low temperatures.

http://iopscience.iop.org/article/10.1088/0022-3719/20/32/013/pdf

Kazutoshi Ohashi

Papers

Thermal expansion of a high purity synthetic diamond single crystal at low temperatures

Transport of heavily boron-doped synthetic semiconductor diamond in the hopping regime

Thermal Expansion Coefficient of Synthetic Diamond Single Crystal at Low Temperatures

Thermal expansion of a boron-doped diamond single crystal at low temperatures

The thermal expansion coefficient and Gruneisen parameter of InP crystal at low temperatures