Synthetic Single Crystals Research Articles

Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series

A multi-analytical approach using electron microprobe analysis, X-ray structural refinement, and optical absorption spectroscopy was applied to characterize short-range and long-range structures of synthetic spinel single crystals along the MgAl2O4-CuAl2O4 solid-solution series. Site populations, derived from the results of site-scattering refinement and stereochemical analysis, show that the tetrahedrally coordinated site (T) is mainly populated by Mg and Cu2+, while the octahedrally coordinated site (M) is dominated by Al. Crystals also show a significant degree of inversion, i.e., occurrence of Al at T counterbalanced by occurrence of divalent cations at M, which increases slightly from 0.24 to 0.29 for the highest Cu2+ contents. Short-range information derived from optical spectra suggests that the local TCu2+-O distances remain constant at increasing Cu2+ content, whereas local MCu2+-O distances are ca. 0.02 Å shorter in Cu-poor MgAl2O4 spinels as compared to MCu2+-O distances in end-member CuAl2O4. The observed splitting of an absorption band, at ca. 7000 cm-1 , caused by electron transitions in TCu2+ as well as the anomalous broadness of an absorption band, at ca. 13 500 cm-1, caused by electron transitions in MCu2+ indicates the occurrence of local Jahn-Teller distortions at T and M. Long-range information, however, shows no violation of Fd3m symmetry. From refinements of our single-crystal XRD data we could for the first time derive for a cubic spinel phase a MCu2+-O distance of 2.080 Å and a TCu2+-O of 1.960 Å. The very limited variations in the unit-cell parameter a from 8.079 to 8.087 Å are mainly related to the disordering of Al. Because of the very similar size of Cu2+ and Mg at the T and M sites, the spinel structure responds to the Cu2+ → Mg substitution by increasing cation disordering in such a manner that mean M-O distances remain constant and the mean T-O distances decrease slightly. This results in increasing length of shared octahedral edges and thereby increase of the octahedral cation-cation repulsion. In line with other studies, the importance of steric factors for controlling the cation distributions in the spinel structure is demonstrated to be valid also in the MgAl2O4-CuAl2O4 solid-solution series.

Orientation, oxygen activity and temperature dependencies of the diffusion of manganese in manganese orthosilicate, Mn2SiO4

The diffusion of manganese in manganese silicate, Mn2SiO4, in equilibrium with MnSiO3 was experimentally studied as a function of crystallographic orientation, oxygen activity and temperature using high purity synthetic single crystals of manganese silicate. The oxygen activity dependence of the manganese cation diffusion in Mn2SiO4 along the three principle orientations at 1200°C suggests that, at high oxygen activities, manganese cations move via different types of vacancies, most likely isolated manganese vacancies, (VMn2+)″, and possibly neutral associates, {2(MnMn2+3+)⋅(VMn2+)″}×, the latter being minority defects. At lower oxygen activities, the oxygen activity dependence of the manganese tracer diffusion becomes smaller than that at higher oxygen activities and eventually becomes negative at very low oxygen activities. The latter is attributed to an increased concentration of manganese interstitials at lower oxygen activities. The temperature dependence of the manganese tracer diffusion along the three principle orientations was experimentally investigated between 1150 and 1250°C at log aO2=−2.7 (aO2=PO2/PO2o with PO2o=1atm) and between 1150 and 1300°C at log aO2=−9.8. The results obtained suggest that the orientation dependence of the diffusion of manganese in Mn2SiO4 does not vary very significantly with temperature. When using the space group Pbnm to describe crystal orientations, the ratio found for the manganese tracer diffusion coefficients at log aO2=−2.7 is approximately DMn[001]∗:DMn[010]∗:DMn[100]∗=5.3:2.2:1.

Diffusion and solubility of hydrogen and water in periclase

Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm−1 indicating VOH− centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structure as a result of proton diffusion into the crystal. For completely equilibrated specimens, the OH-defect concentration, expressed as H2O equivalent, was calculated to 3.5 wt ppm H2O at 1,200 °C and 0.5 GPa based on the calibration method of Libowitzky and Rossmann (Am Min 82:1111–1115, 1997). This value was confirmed via Raman spectroscopy, which shows OH-defect-related bands at identical wavenumbers and yields an H2O equivalent concentration of about 9 wt ppm using the quantification scheme of Thomas et al. (Am Min 93:1550–1557, 2008), revised by Mrosko et al. (Am Mineral 96:1748–1759, 2011). Results of both independent methods give an overall OH-defect concentration range of 3.5–9 (+4.5/−2.6) ppm H2O. Proton diffusion follows an Arrhenius law with an activation energy Ea = 280 ± 64 kJ mol−1 and the logarithm of the pre-exponential factor logDo (m2 s−1) = −2.4 ± 1.9. IR spectra taken close to the rims of MgO crystals that were exposed to water-saturated conditions at 1,200 °C and 0.5 GPa for 24 h show an additional band at 3,697 cm−1, which is related to brucite precipitates. This may be explained by diffusion of molecular water into the periclase, and its reaction with the host crystal during quenching. Diffusion of molecular water may be described by logDH2O (m2 s−1) = −14.1 ± 0.4 (2σ) at 1,200 °C and 0.5 GPa, which is ~ 2 orders of magnitude slower than proton diffusion at identical P-T conditions.

Re-investigation of the crystal structure of enstatite under high-pressure conditions

A synthetic single crystal of pure orthoenstatite (MgSiO3, space group Pbca ) has been investigated at high pressure for structural determinations by in situ single-crystal X-ray diffraction using a diamond-anvil cell. Ten complete intensity data collections were performed up to 9.36 GPa. This study significantly improved the accuracy of structural parameters in comparison to a previous high-pressure structural study, allowing a more detailed examination of structural behavior of orthoenstatite at high pressures and a comparison to other more recent structural studies performed on orthopyroxenes with different compositions. The structural evolution determined in this work confirms the high-pressure evolution found previously for other orthopyroxenes and removes some ambiguities originating from the less accurate published data on the MgSiO3 structure at high pressure. The structural compression is mostly governed by significant volume decrease of the Mg1 and Mg2 octahedra, affecting in turn the kink of the tetrahedral chains, especially the TB chain of larger SiO4 tetrahedra. The Mg2 polyhedron undergoes the largest volume variation, 8.7%, due especially to the strong contraction of the longest bond distance (Mg2-O3B), whereas Mg1 polyhedral volume decreases by about 7.4%. The compressional behavior of the tetrahedral sites is quite different from previously published data. The TA and TB tetrahedral volumes decrease by about 2.8 and 1.8%, respectively, and no discontinuities can be observed in the pressure range investigated. Using the data on the pure orthoenstatite as reference, we can confirm the basic influences of element substitutions on the evolution of the crystal structure with pressure.

Small-scale transport of trace elements Nb and Cr during growth of titanite: an experimental study at 600 °C, 0.4 GPa

Trace element distribution in titanite overgrowths on rutile has been investigated experimentally at 600 °C, 400 MPa and fO2 near NiNiO buffer. Compositionally homogenous Cr- or Nb-doped synthetic rutile single crystals or Nb-containing natural rutile crystals were the source of Cr, Nb and Ti to synthesize titanite using the double-capsule technique. All element exchange with the source of Si, Ca and Al occurred via a NaCl–H2O fluid. Titanite forms quickly and exclusively around the rutile crystals. The titanite overgrowth separates rutile from the bulk fluid, and all elements from rutile dissolution have to pass through the titanite rim. Trace element concentrations in titanite show a considerable scatter in experiments with and without Al, although the average concentrations of Cr or Nb of titanite around compositionally homogeneous synthetic rutile approach the expected values for closed system conditions. Variability of Al with Cr or Nb in the titanite is not correlated. The Al zoning is irregular and patchy, and also the distribution of trace elements does not show systematic trends in the spatial distribution. In experiments using zoned natural rutile, the concentrations of Nb in titanite are related to the Nb zoning in rutile, but the contents also vary unsystematically. Under the controlled conditions of the experiment, the explanation for the strongly irregular spatial distribution is most likely due to variations in elemental concentrations during transport from the rutile along the titanite grain boundaries. The transport pathway is complex because grain boundary migration is important during titanite growth. Such irregular element distribution is also found in a natural sample of titanite overgrowth on rutile from an eclogite with retrograde overprint in the amphibolite facies. Transport of Ti and trace elements was focused on grain boundaries and shielded from the rutile as a source of these elements. We conclude that this type of zoning is not related to changes in P–T or composition in an open system, but solely controlled by transport in and through the titanite rim.

High silicon self-diffusion coefficient in dry forsterite

Silicon self-diffusion coefficients (DSi) in dry synthetic forsterite single crystals were measured at temperatures of 1600 and 1800K, from ambient pressure up to 13GPa using an ambient pressure furnace and Kawai-type multi-anvil apparatus. The water contents in the samples were carefully controlled at <1μg/g. Diffusion profiles were obtained by secondary ion mass spectrometry (SIMS) in depth profiling mode. Small negative pressure dependence of DSi is determined with an activation volume of 1.7±0.4cm3/mol. The activation energy is found to be 410±30kJ/mol. LogDSi values (DSi in m2/s) at 1600 and 1800K at ambient pressure are determined to be −19.7±0.4 and −18.1±0.3, respectively. These values are ∼2.4 orders of magnitude higher than those reported by Jaoul et al. (1981). We speculate that their low DSi might reflect the effects of a horizontal migration of the isotopically enriched thin films applied on the sample surfaces, which may inhibit diffusion into the substrate during annealing. Our results for DSi resolve the inconsistency between DSi measured in diffusion experiments and those deduced from creep rates measured in deformation experiments.

Electrical conductivity of H-bearing orthopyroxene single crystals measured with impedance spectroscopy

In this study, the electrical conductivity of synthetic and natural orthopyroxene single crystals containing various amounts of hydrogen and cation impurities (i.e., Al, Fe) was investigated using impedance spectroscopy. A new cell was developed to measure conductivities of submillimeter-sized oriented single crystals with impedances up to 1010 Ohm. In contrast to previous studies on olivine and orthopyroxene, results from this study do not show a simple correlation of the concentration of protons and the electrical conductivity. Instead, the electrical conductivity appears to be a complex function of iron content, hydrogen content, crystal orientation and concentration of other impurity cations and shows similar activation energies to hydrogen diffusion. Model calculations considering proton conduction rather exclude than suggest orthopyroxene as responsible phase for high-conductivity regions in the Earth’s upper mantle.

Orientation, oxygen activity and temperature dependencies of the diffusion of cobalt in cobalt orthosilicate, Co2SiO4

To contribute to a better understanding of point defects and defect-related transport properties in cobalt orthosilicate, Co2SiO4, the orientation-dependent diffusion of cobalt in high purity, synthetic single crystals of Co2SiO4 being in thermodynamic equilibrium with silica was experimentally studied as a function of crystallographic orientation, oxygen activity and temperature. The oxygen activity dependence of the diffusion of cobalt in Co2SiO4 along the three principle orientations at 1300°C is at high oxygen activities compatible with cobalt vacancies and holes as majority defects. At lower oxygen activities the oxygen activity dependence of the cobalt tracer diffusion coefficients becomes smaller than at high oxygen activities. This is most likely related to an increase of the concentrations of cobalt interstitials at lower oxygen activities and at such oxygen activities also to an increased influence of the impurity ions being present in the samples used. The latter is due to smaller overall point defect concentrations at lower oxygen activities compared to those found at higher oxygen activities. The temperature dependence of the cobalt tracer diffusion along the orientations denoted above was investigated in the range between 1200 and 1300°C at aO2=1 (aO2=PO2/P°O2 and P°O2=1atm). The results obtained suggest that the anisotropy of the diffusion of Co in Co2SiO4 does not very significantly vary with the temperature. When using the space group Pbnm when assigning crystal orientations the ratio found for the cobalt tracer diffusion coefficients at aO2=1 is approximately D⁎Co[001]:D⁎Co[010]:D⁎Co[100]=30:3:1.

Epitaxial synthesis of diamond layers on a monocrystalline diamond substrate in a torch microwave plasmatron

The epitaxial growth of a diamond single-crystal film in a torch microwave discharge excited by a magnetron of a domestic microwave oven with the power of ≤1 kW in an argon-hydrogen-methane mixture with a high concentration of methane (up to 25% with respect to hydrogen) at atmospheric pressure on a sub-strate of a synthetic diamond single crystal (HPHP) with the orientation (100) and 4 × 4 mm in size is obtained. A discharge with the torch diameter of ∼2 mm and the concentration of the microwave power absorbed in the torch volume of >103 W/cm3 is shown to be effective for epitaxial enlargement of a single crystal of synthetic diamond. The structure of the deposited film with the thickness up to 10 μm with high-quality morphology is investigated with an optical microscope as well as using the methods of the Raman scattering and scanning electron microscopy.

Cutting tool material selection using grey complex proportional assessment method

In today’s metalworking industry, many types of materials, ranging from high carbon steel to ceramics and diamonds, are used as cutting tools. Because of the wide range of conditions and requirements, no single cutting tool material meets all the needs of machining applications. Each tool material has its own properties and characteristics that make it best for a specific machining application. While evaluating a cutting tool material for a machining operation, the applicability is dependant on having the correct combination of its physical properties. Thus, it is extensively important to select the most appropriate cutting tool material with the desired properties for enhanced machining performance. This paper considers an exhaustive list of 19 cutting tool materials whose performance are evaluated based on ten selection criteria. The grey complex proportional assessment (COPRAS-G) method is then applied to solve this cutting tool material selection problem considering grey data in the decision matrix. Synthetic single crystal and polycrystal diamonds emerge out as the best two choices. Oil quenched tool steel (AISI O2) and powder metal tool steel (AISI A11) may also be used as the suitable cutting tool materials. Sialon and sintered reaction bonded silicon nitride are the worst chosen cutting tool materials.

Micelles in a crystal

Inclusion of organic molecules in inorganic crystals is thought to enhance their mechanical properties, yet obtaining high occlusion levels has been a challenge. It is now shown that synthetic calcite single crystals incorporating a significant amount of copolymer micelles have mechanical properties similar to biogenic calcite crystals.

Chemical Composition and Structure of the Boride Inclusions in Synthetic Diamonds Grown under HPHT

Boride inclusions in the synthetic diamond single crystals grown from Fe-Ni-C-B system under high temperature and high pressure were studied in the present paper. Both chemical composition and structure of the inclusions incorporated into the diamond during the process of diamond growth were successfully determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the inclusions related to boron trapped in the diamond consisted of f.c.c. (FeNi)23(CB)6, (FeNi)3(CB), Fe2B, FeB, hexagonal Ni3B, and B4C.

Point defects and orientation-dependent transport of matter and charge in iron-containing olivines

The variation of the oxygen content, x O, of synthetic fayalite (Fe 2SiO 4) single crystals was investigated thermogravimetrically at 1130 °C as a function of the oxygen activity, a O 2 (= P O 2 /P O 2 ° ≈ f O 2 /f O 2 ° with P O 2 ° ≈ f O 2 ° = 1 bar ≈ 1 atm). It was found that x O varies less in fayalite single crystals than in polycrystalline Fe 2SiO 4 studied earlier. The majority defects are most likely cation vacancies, (V Me 2+ )″, ferric ions on M-sites, (Fe 3+ Me 2+ ) , and ferric ions on Si-sites, (Fe 3+ Si 4+ )′. Furthermore, the diffusion of iron in synthetic olivine single crystals ((Fe xMg 1 − x ) 2SiO 4) was studied at 1130 °C as a function of orientation, oxygen activity, and cationic composition. The observed oxygen activity dependencies suggest that cations move via different types of cation vacancies, most likely isolated vacancies, (V Fe 2+ )″, and possibly neutral associates, {2(Fe 3+ Me 2+ ) ⋅ (V Me 2+ ) ′ ​ ′ } x, the latter being minority defects. In addition, the electrical conductivity, σ, of fayalite single crystals was investigated as a function of orientation and oxygen activity within the stability field of fayalite at 1130 °C. The observed oxygen activity dependencies are compatible with (V Me 2+ ) ′ ​ ′ , (Fe 3+ Me 2+ ) , and (Fe 3+ Si 4+ )′ being the majority point defects at high a O 2 and with h ⋅ and e′ as the majority defects at low a O 2 . The electrical conduction in fayalite is governed by contributions of electrons and holes. This extended point defect model for fayalite is also compatible with data for the variation of the oxygen content and for the iron tracer diffusion.

Characterization of top-quality type IIa synthetic diamonds for new X-ray optics

We have performed a complex analysis of top-quality synthetic diamond HPHT type IIa single crystals in view of their potential application as X-ray optics elements, namely as free electron laser mirrors. We have employed X-ray topography and high-resolution diffractometry along with optical spectroscopy techniques for characterization of our synthetic diamonds.

Zn-O tetrahedral bond length variations in normal spinel oxides

Six synthetic single crystals of spinel phases with different compositions along the ZnAl 2 O 4 -ZnCr 2 O 4 solid solution were structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. As predicted, unit-cell parameters and octahedral bond lengths (M-O) increase with increasing replacement of Al 3+ by Cr 3+ . Despite the constant occupancy of the T site by Zn, also the tetrahedral bond length T Zn-O shows significant variations along this binary. These variations are positively correlated with variations in M-O bond lengths. The present data in conjunction with data from literature provide a basis for quantitative analyses of the variation in T Zn-O in normal spinel structures. A negative correlation between T Zn-O and the ionic potential at M ( M IP ) suggests that increasing M IP is related to a stronger electrostatic cation-cation repulsion across the shared octahedral edge M (O-O) shared of the structure. An observed negative correlation between M IP and M (O-O) shared suggests that a decrease of M (O-O) shared provides a more efficient shielding effect to reduce the octahedral cation interactions. In normal Zn B 2 O 4 spinels (where B = Al 3+ , Cr 3+ , Ga 3+ , V 3+ , Fe 3+ , and Mn 3+ ) cations with a smaller size provides a higher charge density. Increasing charge density at the M site causes shortening of M (O-O) shared , which in turn results in shorter T Zn-O bond length. In general, variations in T Zn-O are required by the structure to better provide an oxygen shielding effect to the octahedral cation-cation repulsion.

Thermal diffusivity of alkali and silver halide crystals as a function of temperature

The phonon component of thermal diffusivity (D) for ten synthetic single-crystals (LiF, NaCl, NaI, NaI:Tl, KCl, KBr, CsI, CsI:Tl, AgCl, and AgBr) with the B1 and B2 structures was measured from ambient temperature (T) up to ∼1093 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. We investigated optical flats from different manufacturers as well as pellets made from compressed powders of most of the above chemical compositions plus LiI, NaBr, KI, RbCl, RbBr, RbI, CsCl, CsBr, and AgI. Impurities were characterized using various spectroscopic methods. With increasing T,D decreases such that near melting the derivatives ∂D/∂T are low, −0.0006±0.0004 mm2 s−1 K−1. Our results are ∼16% lower than D298 previously obtained with contact methods, which are elevated by ballistic radiative transfer for these infrared (IR) windows, and are well described by either D−1 following a low order polynomial in T, or by D−1∝T+n, where n ranges from 1.0294 to 1.9429. Inverse correlations were found between D298 and both density and thermal expansivity (α). Primitive lattice constant times compressional velocity correlates directly with D but changes much more slowly with temperature. Instead, D(T) is proportional to (TαL)−1 from ∼0 K up to the limit of measurements, in accord with these physical properties being anharmonic. On average, the damped harmonic oscillator–phonon gas model reproduces D298 based on two physical properties: compressional velocity and the damping coefficient (Γ) from analysis of IR reflectivity data. Given large uncertainties in Γ(T), D−1(T) is reproduced for LiF, NaCl, MgO, and the silver halides, for which IR reflectivity data are available. Our correlations show that optical phonons largely govern heat transport of insulators, and permit prediction of D and thus thermal conductivity for simple, diatomic solids.

Solubility of CePO 4 monazite and YPO 4 xenotime in H 2O and H 2O–NaCl at 800 °C and 1 GPa: Implications for REE and Y transport during high-grade metamorphism

Monazite and xenotime are important accessory minerals in metasediments because they host REE and are useful for geochronology and geothermometry. It is therefore essential to understand their behavior during metasomatic processes that attend metamorphism and subduction. In order to constrain the solubility of monazite and YPO 4 xenotime at high pressure and temperature, we carried out weight-loss experiments on synthetic single crystals of CePO 4 (monazite) and YPO 4 (xenotime) using hydrothermal piston-cylinder methods at 800 °C and 1 GPa, in H 2O and H 2O–NaCl fluids. Results indicate that CePO 4 and YPO 4 dissolved congruently, and that their solubilities in pure H 2O are very low: 0.04 ± 0.04 and 0.25 millimolal, respectively. The solubility of CePO 4 rises to an increasing extent with added NaCl, to 7.94 ± 0.07 millimolal at 50 mol% NaCl. In contrast, the solubility of YPO 4 rises to a decreasing degree with increasing NaCl, to 4.36 ± 0.08 millimolal at 50 mol% NaCl. Best fit equations for the solubilities of the two phases are m CePO 4 = 3.56 · 10 − 5 + 5.82 · 10 −3 X NaCl + 1.97 · 10 −2 X 2 NaCl and m YPO 4 = 2.48 · 10 −4 + 1.26 · 10 −2 X NaCl − 8.89 · 10 −3 X 2 NaCl. The solubility of YPO 4 is greater than that of CePO 4 at NaCl mole fractions ( X NaCl) of 0.00–0.27. The solubility enhancement behavior implies that Ce dissolves as anhydrous chloride complexes, whereas Y forms mixed Cl–OH solutes. The results provide a simple mechanism for redistributing REE and Y in deep-crustal and upper mantle environments. The H 2O/Ce ratio inferred for subduction-zone melts and silicate-rich fluids can also be produced by a CePO 4-saturated fluid with X NaCl = 0.1. In addition, neutral-pH H 2O–NaCl fluids can transport substantial REE and Y, obviating the need to invoke highly acid solutions in environments where they are unlikely.

Fabrication of grinding tool material by the SHS of Ni–Al/diamond/dilute

A mixture of Ni–Cr–P, Cu and B powder was used as a dilute for modifying the microstructure of the reacted product and easing the fast propagating rate and the high temperature in the self-propagating high-temperature synthesis (SHS) of Ni–Al matrix grinding tool material. The SHS process of the Ni–Al/diamond/dilute was examined and the microstructure of the reacted product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grinding performance of the tool was tested in the grinding of a synthetic single crystal of sapphire. The results showed that the dilute substantially reduced the propagating rate and the combustion temperature of Ni–Al SHS. Besides the dominating intermetallics NiAl and NiAl 3, Ni 4Al 3 was also identified in the reacted Ni–Al/diamond/dilute composite owing to the Ni rich environment. In the reacted composite there was a Cr-rich zone at the boundary of the diamond grit due to the formation of Cr 3C 2 between Cr and the diamond. In the grinding a lower wear rate and a better retention ability of diamond grits could be achieved for the grinding tool material that contained finer diamond grits.

Kinetics of the low-temperature hydrogen reduction of single-crystal magnetite

The hydrogen reduction of plates made from synthetic magnetite single crystals is studied in the temperature range 400–570°C. A mathematical model is developed and applied to describe the kinetics of gaseous reduction of plane finite objects. The following time contributions of individual process stages are distinguished with the least squares method and numerical integration: the nucleation of an iron phase, a chemical interaction of magnetite with hydrogen, and external and internal mass transfer. The diffusion and kinetic reduction parameters are calculated. The activation energy of the chemical stage (87.5 kJ/mol) is determined. An equation for the rate constant of the interaction of magnetite with hydrogen is proposed for temperatures below 570°C. A significant effect of the processes of consolidation and sintering of reduced iron on the internal diffusion parameters is detected in the low-temperature range.

Acoustic Emission Study of Growth Process of Diamond Crystals under HPHT

The growth process of synthetic diamond single crystals under high-pressure and high-temperature (HPHT) was investigated using acoustic emission (AE) technique. And AE parameters corresponding to growth process were analyzed. However, the AE features of diamond growth are relativelyweak and easily obscured by other AE sources. So the fast Fourier transformation (FFT) was used to calculate the frequency spectra of AE signals for identifying different AE sources. The results showed that the variation of AE counts and energy is in a good agreement with the formation process of synthetic diamond crystals. And the AE signals pronounced from diamond growth are concentrated in the frequency range from 100 to 250 kHz. Thus, AE technique is an effective way to monitor and study the diamond growth, and the frequency analysis can be a useful way to identify different AE sources.