Showing papers on "Time-of-flight diffraction ultrasonics published in 1984"

Experience with the time-of-flight diffraction technique and an accompanying portable and versatile ultrasonic digital recording system

Abstract: Experience acquise avec la technique de diffraction temps de vol et systeme d'enregistrement numerique ultrasonore portable et flexible

Detection and sizing of inner radius defects in DDT plate 4 (simulated PWR nozzle) by the ultrasonic time-of-flight diffraction technique

Abstract: Detection et caracterisation des defauts dans la zone du rayon interieur de la plaque no 4 des essais de detection de defauts (simulation d'un orifice dans un reacteur a eau pressurisee) par la technique ultrasonore de diffraction utilisant le temps de transit

Acousto-optic method for nondestructive testing

Abstract: An alternative method for nondestructive testing based on light diffraction by ultrasonic waves is presented. It enables us to make more accurate measurements of intensity and phase of reflected waves, and therefore detailed information about the reflecting system can be obtained. Applications are numerous but special attention is payed to examination of the quality of coupling systems.

Trithallium tetraselenophosphate, Tl3PSe4, and trithallium tetrathioarsenate, Tl3AsS4, by neutron time-of-flight diffraction

Abstract: Room-temperature (293 K) single-crystal structure determinations of the isostructural materials TlaPSe 4 and T13AsS 4 were performed at the Los Alamos National Laboratory Pulsed Neutron Facility. For TlaPSe4: M r = 9 5 9 . 9 2 , Pcmn, a = 9 . 2 7 6 ( 1 ) , b = 11.036(2), c = 9 . 0 5 8 ( 1 ) A, V = 9 2 7 . 2 7 A 3, Z = 4 , D m -= 6.87 (2), D x = 6.876 Mg m -a, ,;I, neutron = 0.5--*5.2 A, F(000) = 252.5 fm. For T13AsS4: M r = 816.29, Pcmn, a = 9 . 0 8 4 ( 3 ) , b = 1 0 . 8 7 7 ( 3 ) , c = 8.877 (3)./k, V = 8 7 7 . 1 1 A 3, Z = 4 , D ~ = 6.18 (2), D x = 6.181 Mg m -3, 2neutron = 0.5--*5"2 A, F(000) = 177-2 fm. For T13PSe 4 (TlaAsS4), 1929 (1013) reflections were measured with I > 3a(/) and refined by full-matrix least squares to R ( F ) = 0 . 0 6 1 (0.063). Results on atomic refinement from this study represent an order of magnitude increase in precision over 0108-2701/84/091502-05501.50 © 1984 International Union of Crystallography R. W. ALKIRE, P. J. VERGAMINI, A. C. LARSON AND B. MOROSIN 1503 previous single-crystal X-ray structural work using Mo Ka radiation. The PSe4 a(ASS43-) groups have essentially tetrahedral configurations and one T1 + ion shows large anisotropic thermal motion which is structure related. Introduction. TlaPSe 4 and TIaAsS 4 are two members of a large family of chalcogenide crystals (T13AsSe3, TlaVS 4, TIGaSe2, AgAsS 3 and others) which have potential applications in acousto-optic devices. Such devices include optical filters, laser modulators, deflectors and signal processors, to name a few. These isostructural materials are particularly important because their optical transmission is quite high (6090% in the 0.8 8 fxrn region) and their acoustic (shear-wave) velocities are among the lowest of any solid or liquid recorded in the literature, apart from those velocities associated with critical-point phenomena. Low acoustic-wave velocities also make these materials potentially useful for miniature delay lines. For example, by using the slow shear mode in TI3PSe 4 (1.2 × 105 cm s -1 [001] propagation direction) it is possible to produce a 10 ~ts delay using a crystal that is only 5 mm long (Gottlieb, Isaacs, Feichtner & Roland, 1974). Interest in these materials has also been generated by the discovery of pressure-induced structural phase transitions with related softening of the anomalous shear mode. These transitions were confirmed for Wl3PSe 4 (Fritz, Isaacs, Gottlieb & Morosin, 1978) and TI3AsS 4 (Fritz, Gottlieb, Isaacs & Morosin, 1981)using ultrasonic (pulse echo) techniques and appear to be completely reversible. Measurements on T13PSe 4 as a function of temperature also show a linear decrease in the ab shear mode velocity, but no temperature-induced structural phase transition has been observed (Fritz et al., 1978). Atomic positions were originally determined for these compounds using Mo Ka radiation (Fritz et al., 1978). These compounds are relatively soft, however, and morphology of the single-crystal specimens used was ill defined. Consequently, correcting measured intensities for absorption proved difficult [e.g. # ( M o K a ) = 1250 cm -1 for TI3AsS 4] and led to rather high standard deviations on the atomic positions. In order to reduce uncertainties in atomic positions as well as obtain meaningful thermal parameters which might offer insight into the incipient lattice instability associated with ultrasonic measurements, both structures were redetermined using single-crystal neutron diffraction data. Time-of-flight diffraction Single-crystal neutron diffraction using the timeof-flight technique was explored as early as 1965 (Buras, Mikke, Lebech & Leciejewicz, 1965) on a steady-state reactor. With the advent of pulsed neutron sources (Peterson, Reis, Schultz & Day, 1980; Carpenter, 1977) much effort has been devoted to developing the time-of-flight technique for routine single-crystal structure analysis (Day, Johnson & Sinclair, 1969; Lebech, Mikke & Sledziewska-Blocka, 1970; Day & Sinclair, 1970; Niimura, Kubota, Sato, Arai & Ishikawa, 1980; Schultz, Teller, Peterson & Williams, 1982; Larson & Vergamini, 1981). Recent advances at Los Alamos National Laboratory (Larson & Vergamini, 1982) and elsewhere (Schultz, Teller, Beno, Williams, Brookhart, Lamanna & Humphrey, 1983) have refined the technique so that routine crystal structure analysis is now possible. The time-of-flight technique is considerably different from conventional diffraction techniques in that the Laue method is used for measuring Bragg diffracted intensities. Here, the crystal is stationary and the detector is set at a fixed 20 angle. According to Bragg's Law (n2 = 2dsin0), all orders (n) of a Bragg plane diffract energy at wavelengths 21/n (21 is the first order) and each of these orders hits the same spot on the detector. Obvious difficulties are encountered if polychromatic X-rays are used in the experiment since all diffraction maxima from a single Bragg plane occur simultaneously on the detector (commonly one spot on a film). Discrete wavelength information is lost and, therefore, so is the ability to separate individual hkl intensities. With pulsed neutron sources wavelength information is retained. Polychromatic neutrons produced in a single burst leave the target moderator and, due to differences in their velocities, are separated by time-of-flight over a fixed moderator to detector distance. Quantitative integrated intensities can be measured, then, because each solution (2Jn) to the Bragg equation arrives at the detector separated in time. In addition to collecting multi-wavelength data, enhanced data-collection rates can be achieved by utilizing a two-dimensional (spatial) area detector; this allows a large section of reciprocal space to be examined with a single, fixed setting of the crystal. Each such setting (histogram) measures all the diffracted intensity as well as systematic absences in a particular volume of reciprocal space (defined by the wavelength range, crystal orientation, and instrument parameters). Depending on the instrument settings, a full set of data for an orthorhombic crystal (including some overlap of adjacent histograms to ensure complete coverage of all unique data) can typically be measured with twelve crystal settings. Experimental. Single crystals of TlaPSe 4 (TI3AsS4) 2.96 x 2.86 x 2.86 mm (2.90 x 2.80 x 2 .60mm) mounted on a GE quarter circle* with a detection * The single-crystal diffractometer at LANL has been redesigned since completion of this work and will support low-temperature capabilities. Specialized apparatus is also being designed for high-pressure and high-temperature work. 1504 T13PSe 4 AND T13AsS 4 system consisting of a Borkowski-Kopp-type positionsensitive proportional counter (Borkowski & Kopp, 1978) filled with 2 x 10 SPa of 3 H e + X e + C O 2. Detector center (active area 25 x 25 cm) was located 90 ° to the incident beam and 26 cm from the crystal; crystal to moderator distance was 578 cm. Each event on the detector was encoded within a framework consisting of 64 × 64 spatial (or x,y) channels and a time resolution of 128 channels covering the wavelength range 0.5--,5.2 A. Time channels were divided into nearly equal increments of l id and individual x,y channels were equally spaced across the detector. Initial lattice parameters were taken from the X-ray structure and further refined using peak intensities from 100 reflections measured in the range 66-,114 ° (20). Space group Pcmn (cba setting of Pnma; general positions +x,y,z; +r-x, y, ~+z, ~ 1 . + x,1⁄2-y,z; I 1 1 + : x , : y , : + z ) has been retained for these structures to remain consistent with earlier X-ray work as well as with rules suggested by Kennard, Speakman & Donnay (1967); neutron transmission values range from 0.87 to 0.75 (0.94 to 0.89). Densities were measured by Berman torsion balance. Conversion of integrated intensities to structure factor amplitudes is based on the Laue formula (Buras et al., 1965; Schultz et al., 1982) Ihk I kT(o(2)e(~,)A (,~,)y l Fhkl 1224/sin20, where k is the scale factor, T the normalized monitor count, Fhk t the structure factor, 0 the Bragg angle, ~0(2) the incident neutron flux, e(2) the detector efficiency, A (2) the absorption correction for wavelength 2, and y the extinction correction. ~0(2) and 8(2) were obtained as a single normalization factor from incoherent scattering off a 3 mm diameter vanadium bead (Lebech et al., 1970; Day et al., 1969); the vanadium bead is doped with 5.5 at. % niobium to form a composite null coherent scatterer. Absence of neutron resonances (Mughabghab & Garber, 1973; Garber & Kinsey, 1976) in the 0.5--,5.2 ,/~ wavelength range for T1, P, Se, As and S allows linear absorption coefficients to be calculated as follows: TlaPSe4: f i (cm-~)=0.286+ 0.0692; TI3AsS4: fi(cm -~) = 0.179 + 0.0212. Approximately two independent units of data were collected for TI3PSe 4 covering h = +15, k = 3 , 19, l = 3 , 15 with 3213 reflections measured, 1929 observed [ I > 3tr(/)]; approximately one independent unit was measured on TI3AsS 4, h = -14 , 2, k = -19 , 2, l = -14 , 2 with 1746 reflections measured, 1013 observed [ I > 3a(/)]; max. sin0/2 used in the least-squares refinement was 1.00 (1.00) A -~. Due to the variation of extinction and absorption with wavelength in timeof-flight diffraction, all measured reflections were treated as independent observations, i.e. 'equivalent' reflections were not averaged. Data reduction and least-squares refinement were performed using the Los Alamos crystal structure programs (Larson, 1977). Refinements of both structures were carried out using anisotropic temperature factors and an isotropic extinction parameter. The extinction correction Yi is based on the formula (Becker & Coppens, 1974a,b)