Longitudinal Ultrasonic Velocity Research Articles

Ultrasonic studies of the spin-state transition and the local distortion in LaCoO3

Temperature dependence of longitudinal and transverse ultrasonic velocities and attenuations of the single-phase polycrystalline LaCoO3 were presente d. A clear softening in the longitudinal ultrasonic velocity accompanied by a sharp peak in attenuation were observed near the spin-state transition temperature(≈90K), which did not appear in the transverse mode measurement. This anomalous ultraso nic behavior further demonstrates that the spin-state transition of Co3+ ions in LaCoO3 near 90K are more likely from a low spin state (LS,t62ge 0g) to an intermediate spin state (IS,t5 2ge1g ) than to a high s pin state (HS,t42ge2g ). A b ig attenuation peak accompanied by a slight softening in velocity was observed near 200K in both longitudinal and tr ansverse modes, which was probably caused by the relaxation of the local distort ions originating from Jahn-Teller effect of the randomly distributed IS state Co 3+ ions.

Ultrasonic velocity in Zn substituted GdBaSrCu 3O 7−δ superconductor

Longitudinal and shear ultrasonic velocity in Zn substituted GdBaSr(Cu 3− x Zn x )O 7− δ ( x = 0 , 0.01, 0.03, 0.06 and 0.1) superconductors have been measured using the pulsed-echo-overlap method with frequency 5–10 MHz in the temperature range of 80–300 K. An elastic anomaly characterized by a slope change was observed in the x = 0 sample in the longitudinal mode at around 220 K. This anomaly shifts towards lower temperature with increasing Zn content and vanishes when x = 0.06 and 0.1. The characteristic Debye temperature and electron–phonon coupling constant were estimated using the standard BCS theory as well as the two-dimensional van Hove scenario. The variation in the elastic behaviours upon Zn doping may be due to the effect of changes in the spin correlation at the CuO 2 planes.

Ultrasonic studies on network structure of ternary TeO 2–WO 3–K 2O glass system

Longitudinal and shear ultrasonic velocities were measured in different compositions of the glass system (TeO 2) 80–(WO 3) (20− x) –(K 2O) x using pulse echo technique. Measurements were carried out at 6 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as, glass transition temperature, Debye temperature, softening temperature, and fugacity have been calculated. Results indicated that these parameters depend upon the alkali oxide modifier (K 2O) content i.e., glass composition. Quantitative analysis has been carried out, in order to obtain more informations about the structure of these glasses, based on bond compression model, and ring deformation model, i.e., the cation-anion bond of each oxide.

The use of ultrasonic properties of cr-39 track detectors in neutron dosimetry

The longitudinal and shear wave ultrasonic velocities have been measured before and after exposing 5-mm thick CR-39 solid state nuclear track detectors to both a mixed field of γ-rays and fast neutrons from an Am-Be source in the ranges from 0 to 104 mSv. The change in the intermolecular structure as caused by the fast neutron exposure was studied by the ultrasonic pulse echo method at a frequency of 2 MHz and at room temperature. The elastic coefficients, Poisson's ratio, microhardness, ultrasonic absorption coefficient and internal friction have been determined. The study shows that the γ-ray irradiation had no effect on the ultrasonic properties of CR-39 at least at the used doses. However, all the ultrasonic properties are influenced by the fast neutrons at doses up to 104 mSv. Our experimental results confirmed that the ultrasonic technique is useful for fast neutron detection, by exploiting the differences in mechanical properties of CR-39.

Ultrasonic study and physical properties of some borate glasses

The structure of the glass system (75− x)B 2O 3– xBi 2O 3–25Li 2O, where x=5, 10, 15, and 20 mol% was investigated by using pulse-echo technique. Elastic properties of the glass system have been calculated together with Poisson’s ratio and Debye temperature from the measured densities as well as longitudinal and shear ultrasonic velocities at room temperature. Ultrasonic velocity measurements were taken at 4 MHz. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Addition effect of Bi 2O 3 on the elastic moduli was investigated in terms of the number of network bonds and the mean cross-link density of the glass systems. The average atomic ring size of the network was also calculated and it was found that it depends on the concentration of the modifiers. Composition dependence of the elastic moduli and Poisson’s ratio from one hand and the trend of both the ring diameter and the packing density from the other hand showed structural change at x=15 mol%.

Strong magnetoelastic effect in Pr1−xCaxMnO3

Manganese oxides with distorted perovskite structure have attracted much attention during the last decade due to their colossal magnetoresistance (CMR), and the strong correlations among the various degrees of freedom involved. In particular, Pr 1-x Ca x MnO 3 compounds present in a wide Ca-doping range a charge ordering phenomenon, consisting of real space ordering of Mu 3+ and Mn 4+ in alternate lattice sites below a certain temperature T CO . This ordering brings about a lattice distortion and a large hardening of the sound velocity below T CO . Tomioka et al. have observed that an applied magnetic field can melt this charge ordered state and induce a transition from an insulating to a metallic state. In order to study the effects of this charge order melting, ultrasonic longitudinal sound velocity measurements were performed on polycrystalline Pr 1-x Ca x MnO 3 (x = 0.35 and 0.5) as a function of magnetic field and temperature. Interesting anomalies were found related to the melting of the charge ordered phase into a metal-like state even at low temperatures.

Characteristics of residual stress in Mo–Ti functionally graded material with a continuous change of composition

With the addition of the sintering additives Ni and Cu, highly dense Mo–Ti alloys with various Mo:Ti ratios were obtained by hot-pressing method. Under the same conditions a Mo–Ti green body with continuously graded composition, formed by the particle settling method, was sintered. The longitudinal and transverse ultrasonic velocities of Mo–Ti alloys were tested in order to calculate the residual stresses that develop during cooling of the Mo–Ti functionally graded material (FGM). By using an axisymmetric finite element method, the fabricated thermal stress in a disk-shaped Mo–Ti FGM was calculated. The results show that the residual stress continuously changes with the smooth change of graded composition and the maximum value of residual tensile stress is far lower than that of the bending strength of Mo–Ti alloys.

Ultrasonic velocity and elastic moduli of heavy metal tellurite glasses

Longitudinal and transverse ultrasonic waves velocities in lead tungsten tellurite glasses have been measured using the pulse-echo method at 5MHz frequency and at room temperature (300K). The elastic properties; longitudinal modulus, shear modulus, Young’s modulus, bulk modulus and Poisson’s ratio together with the microhardness, softening temperature, and Debye temperature are found to be rather sensitive to the glass composition. Information about the structure of the glass can be deduced after calculating the average stretching force constant and the average ring size. A comparison between the experimental elastic moduli data obtained in this study and those calculated theoretically by other models has been discussed.

ELASTIC PROPERTIES OF THE Zn SUBSTITUTED ErBa2Cu3O7-δ SUPERCONDUCTOR

Ultrasonic longitudinal and shear velocity in superconducting ErBa 2( Cu 3-x Zn x) O 7-δ (x = 0, 0.01 and 0.05) have been measured using the pulse-echo-overlap method at frequency 5–10 MHz in the temperature range 80–300 K. Longitudinal velocity hysteresis and elastic anomaly were observed in the x = 0 sample. Similar hysteresis was not observed in the x = 0.01 and 0.05 samples. The characteristic Debye temperature and electron–phonon coupling constant were calculated. The absence of hysteresis for longitudinal velocity in the x = 0.01 and 0.05 samples may be due to the spin correlation at the CuO 2 planes which affects the electron–phonon interaction.

Temperature-dependent ultrasonic study on parity-violating phase transitions of d- and l-alanine single crystals

Ultrasonic technology was utilized to probe the molecular parity violation on phase transitions of alanine enantiomers. Temperature-dependent longitudinal ultrasonic attenuation and velocity were measured in D- and L-alanine single crystals in the range of 200 K to 290 K. The D-alanine crystal showed a reversible second-order phase transition at 247 K, which was accompanied by a pronounced attenuation peak during both heating and cooling. The L-alanine crystal had a step-like attenuation transition also around 247 K, with a thermal hysteresis. Based on the established obvious difference of electron and nucleus spin properties between alanine enantiomers during the phase transition processes, which were unraveled by temperature dependent DC-magnetic susceptibility and 1H CRAMPS ssNMR spectra experiments, spin-phonon coupling is proposed to account for the different ultrasonic velocity and attenuation behaviors between D- and L-alanine crystals near the transition temperature. The present ultrasonic study will mutually support and further correlate itself with previously conducted magnetic susceptibility and ssNMR spectra measurements in the perspective of both electron and nucleus spin properties of enantiomers.

Instrumented Indentation and Ultrasonic Velocity Techniques for the Evaluation of Creep Cavitation in Silicon Nitride

Instrumented indentation and ultrasonic wave velocity techniques combined with precise density change measurements and transmission electron microscopy (TEM) were used to investigate the changes of elastic moduli in silicon nitride after tensile deformation up to 3%. Linear dependencies on strain were also found for the degradation of the indentation modulus, longitudinal and transverse ultrasonic wave velocities, Young's, shear and bulk moduli and Poisson's ratio. The results obtained by indentation technique and ultrasonic method were essentially identical. TEM observation confirmed that multigrain junction cavities were responsible for the density changes and the elastic moduli degradation. The density changes were linearly proportional to tensile strain with the slope of 0.75. Thus, cavitation is the dominant creep mechanism in silicon nitride studied. Instrumented indentation and ultrasound velocity techniques are suitable for non-destructive monitoring of creep damage accumulation in ceramic components.

Ultrasonic properties of fluorosilicate glass-ceramics at cryogenic temperatures

The longitudinal ultrasonic wave velocity and attenuation, and shear wave velocity for machinable fluorosilicate glass-ceramic (MACOR) samples (regular shelf stock, annealed to 900°C, and 1000°C for 10 hrs) were measured as the functions of frequency and temperature with the pulse-echo method. The frequency and temperature range used were 5 MHz to 50 MHz, and 100 K to 300 K respectively. Both velocities for three samples decrease linearly with temperature, and the ultrasonic attenuation increases linearly with the frequency square, and decreases monotonically with increasing temperature. These data were used to calculate the elastic moduli, Lame parameter, and Poisson's ratio for the materials.

Improvement of the compatibility of natural rubber/ethylene–propylene diene monomer rubber blends via natural rubber epoxidation

AbstractThe longitudinal ultrasonic velocity, longitudinal ultrasonic absorption (attenuation coefficient), glass‐transition temperature, and Mooney viscosity for epoxidized natural rubber/ethylene–propylene diene monomer blends were measured. The variation of the longitudinal ultrasonic velocity with the blend ratios was linear, indicating a compatible system in comparison with the same system without epoxidation (natural rubber/ethylene–propylene diene monomer), which was incompatible. Also, the behavior was confirmed by heat of mixing calculations as well as Mooney viscosity measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2816–2819, 2002

Ultrasonic study of the Nd 0.5Sr 0.5MnO 3 manganite

The resistivity, ac susceptibility and ultrasonic sound velocities have been measured for the single-phase Nd 0.5Sr 0.5MnO 3 bulk sample. With decreasing temperature both the transverse and longitudinal ultrasonic sound velocities show two large stiffening stages just below the ferromagnetic transition temperature T C and the charge ordering transition temperature T CO, respectively. The sound velocity stiffening below T C was interpreted in terms of a significant decrease of the static Jahn–Teller distortion of the MnO 6 octahedra due to the spin-lattice coupling, whereas the dramatic sound velocity stiffening below T CO was attributed to the formation of coherent static Jahn–Teller distortion of the MnO 6 octahedra associated with the charge ordering. In an applied magnetic field of 0.5 T, the stiffening of the sound velocity near T CO shifts noticeably to a lower temperature.

Compatibility studies on some rubber blend systems by ultrasonic techniques

Longitudinal ultrasonic velocity, and ultrasonic attenuation, were measured in Adiprene CM–NBR, Adiprene CM–NR, Adiprene E–NR, Adiprene E–NBR blend systems at room temperature, using pulse echo technique. The densities of the blend samples were measured by the immersion method. Glass transition temperatures were measured experimentally using ultrasonic and differential scanning calorimetry (DSC). Glass transition temperatures were also calculated theoretically. Results showed that the variation of both longitudinal ultrasonic velocity and density with composition is linear with Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR blends indicating compatible systems. For Adiprene E–NR, the plots of ultrasonic velocity and density vs. composition deviate from linearity according to the incompatibility degree of this system. Results obtained from ultrasonic attenuation measurements showed that the excess variation of ultrasonic attenuation with composition in rubber blend samples is of relaxational type and only one maxima or minima appeared in case of compatible blends and two or more maxima or minima appeared in case of incompatible blends. The presence of a single transition temperatures observed in DSC thermograms and ultrasonic attenuation–temperature relation is a decisive confirmation of the formation of one single phase and therefore the compatibility behaviour of this blend. On the other hand, the presence of two transition temperatures is taken as evidence of phase separation and consequently the formation of two phases with incompatible behaviour of the blend system.

Anharmonicity and fragility in lithium borate glasses

Since the physical properties of lithium borate glasses xLi2O-(1-x)B2O3 (0<x< 0.28) vary over a wide range with the composition, this binary system is particularly suitable for studying the relationship between vibrational anharmonicity and fragility. The density, the linear expansion coefficient, the longitudinal and transverse ultrasonic velocities and their respective temperature coefficients of the velocities are measured, from which the vibrational anharmonicity in lithium borate glasses is evaluated with the help of the Gruneisen parameter at the Debye cut-off frequency and the Anderson-Gruneisen parameter: these two parameters plotted vs. composition have the same characteristics with minima at x≈0.08. The fragility is evaluated from the temperature width of the glass transition; the fragility also shows a minimum at x≈0.08. The presence of minima at x≈0.08 is ascribable to the fact that the crosslinking density between six-membered rings in the glass reaches a maximum at this composition. We show that the anharmonic parameters strongly correlate with the fragility metrics.

Anharmonicity of quasi-lattice vibrations in glasses of the As(Sb)-O-I(Br, Cl) system in the framework of the fluctuation hole model

Parameters of the free volume theory (such as the fraction of the fluctuation free volume, the hole volume, the energy of hole formation, and the maximum internal pressure) are calculated from the experimental data on the density, microhardness, glass transition temperature, and longitudinal and transverse ultrasonic velocities. The anharmonicity of particle vibrations and the nonlinearity of interatomic interaction forces in vitreous oxides and oxyhalides are considered in the framework of the free volume concept. The relation of the critical strains of the interatomic bonds and the volume strain of the glass network to the lattice Gruneisen parameter is analyzed. The quantities calculated from the thermodynamic Gruneisen equation with the formulas relating the Gruneisen parameter to the Poisson ratio and the fraction of the fluctuation free volume are compared with those determined from the dependences of the elastic modulus on microhardness. A correlation between the parameters of the free volume model and the models based on modern structural concepts of inorganic glasses is discussed.

Determination of the elastic constants of metal-matrix composites by a laser ultrasound technique

The longitudinal and transverse ultrasonic wave velocities of a series of as-cast short-Al 2O 3-fiber-reinforced SAE321 matrix composites (Al 2O 3f/SAE321) and SiC-particle-reinforced ZA-27 matrix composites (SiCp/ZA-27) in the as-cast conditions were measured by a laser ultrasound technique. The experimental results showed that the wave velocities in two composites varied with the volume fraction, f, and the size of the ceramic reinforcements within the metal matrix. The interfacial structures and metallurgical defects of the composite played an important role in the variation of ultrasonic wave velocities. The effective elastic constants of the composites, including Young's modulus, E, the shear modulus, G, Poisson's ratio, ν, and the Lamé coefficient, λ, were calculated by using the values of the velocities and the mass densities of composites according to the elastic theory of solids. As expected, the Young's modulus and shear modulus of as-cast Al 2O 3f/SAE321 composites monotonically increased with increasing volume fraction of the reinforcement. The elastic constants of SiCp/ZA-27 composite with a volume fraction of 0.05 in the as-cast conditions were essentially larger than that of the monolithic alloy and tended to increase with the particle size. However, property deterioration was observed when the particle volume fraction was above this level. It is believed that a thin layer of oxidation inclusions and microvoids at the interface observed by transmission electron microscopy (TEM) as well as metallurgical defects (SiC particle segregation, shrinkage pores and gas-blows) by scanning electron microscopy (SEM) may be responsible for the property degradation.

The Jahn-Tellereffect and electron-phonon interaction inLa0.25Ca0.75Mn1-xCrxO3

The ultrasonic (longitudinal and transverse) velocities and thetransport and magnetic properties of polycrystallineLa0.25Ca0.75Mn1-xCrxO3 (x = 0, 0.03, 0.05,and 0.07) have been studied systematically. It was found that withincreasing Cr content, the resistivity increases, the charge-ordering transition temperature TCO shifts to low temperature,and the magnetic moment of the system is strengthened. From thetemperature dependence of the ultrasonic velocities, one canestablish that the Jahn-Teller energy and phonon exchange constantdecrease with increasing Cr content.

Laser ultrasonic sensing of the melting and solidification of cadmium telluride

A noninvasive laser ultrasonic method has been used to investigate the melting and solidification of a (Cd,Zn)Te alloy during vertical Bridgman growth. A single zone vertical Bridgman furnace was integrated with a laser ultrasonic system and used to monitor the time-of-flight of ultrasonic pulses that propagate across an ampoule during the melting and solidification of Cd 0.96Zn 0.04Te. The measurement approach is based upon the difference in the elastic stiffness of the solid and liquid phases of Cd 0.96Zn 0.04Te (Queheillalt et al., J. Appl. Phys. 83 (1998) 4124) and its significant dependence upon temperature. This results in a reduction of the longitudinal wave ultrasonic velocity as the temperature was increased (from ambient temperature) followed by a ∼ 45% decrease upon melting. The laser ultrasonic sensor provided a robust in-situ method for monitoring the melting and solidification of Cd 0.96Zn 0.04Te. The data indicated that the melting was slow and that solidification was accompanied by a 10–15°C undercooling.