Re: What are the properties of diamond?

Starting around 1000 C in air or 1800 C in a neutral or reducing atmosphere, diamond undergoes catastrophic allotropic conversion to graphite. High temp thermodynamic data is therefore mostly compiled for graphite.

Carbon phase diagram
Carbon crystal structures
Diamond and graphite crystal lattice VRML graphics

            Enthalpy of  Enthalpy of  Entropy   Free Energy of
            combustion   Formation      /_\S    Formation, /_\G
             Kcal/mole                cal/mole    Kcal/mole   
                                                  
Graphite      93.983      0.00       1.3603         -      
Diamond       94.437      0.4540     0.58267      0.684

Temp   Equilibrium constant
        graphite/diamond
 298K       3.18
1273K       1.31
1698K       1.23


Carbon crystal structure (cell dimensions/pm unless otherwise 
stated),space group
        Cubic diamond (a=0.356688 nm), Fd3m, 0.154450 nm bond
         atoms at (000),(0.5,0.5,0),(0,0.5,0.5),(0.5,0,0.5),
                  (0.25,0.25,0.25),(0.75,0.75,0.25),
                  (0.25,0.75,0.75),(0.75,0.25,0.75)
        Hexagonal graphite (a=246.12,c=670.78),P6_3mc
        Rhombohedral graphite (a=364.2,alpha=39deg30'), R3m
        Hexagonal diamond (a=252,c=412),P6_3/mmc
        Hexagonal (a=894.8, c=1408)

Melting point C: 3820 (diam.); 3800 (graph.); 800 K sublimes 
Boiling point, 5100 K
Debye temperature, 402 K (graphite)
 5.7 perpendicular, 1960 parallel (graphite) [298 K] W/m-K
enthalpy of fusion, 105.1 kJ/mol (graphite)
enthalpy of vaporization, 710.9 kJ/mol (graphite)


                   IMPORTANT PROPERTIES OF DIAMOND

(1 GPa = 145,078 psi)
(1 GPa = 10^10 dyne/cm^2)

PROPERTY                                 VALUE

Hardness                           10,000     kg/mm^2
        			       90     GPa
                                5500-8500     Knoop
   (Al203 2000, BC 2250, SiC 1875-3980, WC/TiC 2190, VC 2080)
Strength, tensile                      >1.2   GPa
Strength, compressive                >110     GPa
Compressibility
 Linear                              7.54x10(-11)/Pascal
 Volume                              2.26x10(-10)/Pascal
   (W 3.3x10^(-7) cm^2/kg)
Sound velocity                     18,000     m/sec
Density                                 3.515 g/cm^3
Young's modulus                         1.22  GPa
Elastic Moduli   C11=10.79 C12=1.24 C44=5.96  x10^12 dynes/cm^2
Bulk modulus			4.42x10^12    x10^12 dynes/cm^2
   (W 2.99x10^12 dynes/cm^2)
Poisson's ratio                         0.2  
Thermal expansion coefficient, 20 C 0.8-1.1   ppm/K (re Invar)
                             -100 C 0.4       ppm/K (re silica)
                          100-900 C 1.5-4.8   ppm/K
Thermal conductivity                 2000.0   W/cm-K
 Type I,    20 C                        9     W/cm-K
 Type IIa,  20 C                       26     W/cm-K
 Type I,   190 C                       24     W/cm-K
 Type IIa, 190 C                      120     W/cm-K
 (Cu or SiC, 20C                        4     W/cm-K)
Thermal shock parameter            3x10^7     W/m
Debye temperature, 0 K               2200     K
                   0-800 C           1860     K
Specific Heat, 20 C                     0.113 cal/gm-K
Optical transmissivity                225     nm to far infrared
Loss tangent at 40 Hz                   0.0006  
Dielectric constant                     5.68  0-3 KHz
Dielectric strength                   10^7    V/cm
Electron mobility                    2200     cm^2/V-sec
Hole mobility                        1600     cm^2/V-sec
Electron saturated velocity       2.7x10^7    cm/sec
Hole saturated velocity               10^7    cm/sec
Work function                          <0     V (on [111] surface)
Bandgap                                 5.45  eV
Resistivity                   10^13 - 10^16   ohm-cm
Transparency, IIa                       225 - 2500 nm, >6000 nm
              Ia                        340 - 2500 nm, >10,000 nm
Refractive index                        2.4173 (Na 589.32 nm)
                                        2.4237 (Hg 546.1 nm)
                                        2.4099 (H-alpha 656.3 nm)
                                        2.7151 (226.5 cutoff)

n^2 = 1 + [(0.3306)(l^2)/[(l^2)-3.0625x10^6)] + 
          [(4.3356)(l^2)/[(l^2)-1.1236x10^6)]

n=refractive index, l=wavelength, angstroms
Z. Phys. 15 358 (1923)

Crystal structure:   Phil. Trans. Roy. Soc. A 240 219 (1947)
                     Am. Min. 42 39 (1957)
Density:             J. Appl. Phys. 35 1773 (1964)
Thermal expansion:   Phil. Kag. 1 409 (1956)
                     Am. Min. 42 39 (1957)
Specific Heat:       Phys. Rev. 111 1275 (1958)
                     Phil. Mag. 3 43 (1958)
                     J. Chem. Phys. 36 1903 (1962)
Hardness:            J. Res. Nat. Bur. Standards 23 (1939)
Elastic Properties:  J. Applied Physics 43 2944 (1972)    
                     Proc. Roy. Soc. A 187 381 (1946)    
                     Acta Cryst. 6 450 (1953)            
                     Phys. Rev. 105 116 (1957)           

The bandgap of diamond at ambient is 5.45 eV. The energy of the 
boron impurity level in diamond is 0.37 eV above the valence 
band.  Depending on how much and how N goes into diamond the 
energy level is somewhere between 1.7 and 2.0 below the 
conduction band.

(The experiment was done by JPL in the 92 to 95 timeframe and 
reported in several journals.  Measurements were made to 1100 or 
1200 C for both nitrogen doped and undoped diamond.)

"Typical" N-doped diamond has a resistivity of 10^18 ohm-cm at 
ambient.  Type IIb 10-1000 ohm-cm.  Strong photoconductivity with 
UV.  Changing the temperature gives you a factor of exp(-T1/T2), 
T in degrees K.   At 1000 C therefore about 10^16 ohm-cm.  

--
Uncle Al
Do something naughty to physics