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'Perturbed Angular Correlations' in keywords
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2000 (6)
1998 (2)
1996 (2)
1Author    GaryL. Catchen, EdwardF. Hollinger, ToddM. RearickRequires cookie*
 Title    Characterizing Phase Transitions in the Perovskites PbTi0 3 and BaTi0 3 Using Perturbed-Angular-Correlation Spectroscopy  
 Abstract    Perturbed-angular-correlation (PAC) spectroscopy was used to measure in ceramic samples of PbTi0 3 and BaTi0 3 the temperature dependence of the Ti-site electric-field gradients (EFGs) at temperatures very close to the ferroelectric-to-paraelectric transition temperatures T c . The samples were doped with small amounts of Hf that carried the 181 Hf — l8l Ta probe radioactivity. A high-frequency nuclear quadrupole interaction that decreases very little as the temperature approaches T c , characterizes the PbTi0 3 transition. The tetragonal and cubic phases for PbTi0 3 appear to coexist over a temperature interval of 8 ± 1 K, and the transition shows a thermal hysteresis of about 4 K. In contrast, a lower-frequency interaction that decreases rapidly as temperature approaches T c , characterizes the BaTiO, transition. Both phases of BaTi0 3 appear to coexist over an interval of about 2 K, and the thermal hysteresis is about 1 K. At temperatures above T c , both PbTi0 3 and BaTi0 3 show weak, non-vanishing Ti-site EFGs. Although, for BaTi0 3 , this effect limits the accuracy with which critical effects can be measured, we estimate a power-law exponent ß = 0.21 ± 0.05, which most likely is somewhat lower in magnitude than the actual critical exponent. For the explanation of our observations we assume the existence of a distribution of T c -values. This distribution would arise because the crystals could have spatially non-uniform distributions of nucleation sites, which for PbTi0 3 and BaTi0 3 could be point defects. 
  Reference    Z. Naturforsch. 51a, 411—421 (1996); received November 20 1995 
  Published    1996 
  Keywords    Ferroelectric, perovskite, nuclear electric-quadrupole, perturbed-angular-correlations, phase transition 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0411.pdf 
 Identifier    ZNA-1996-51a-0411 
 Volume    51 
2Author    P. Wodniecki, A. Kulińska, B. Wodniecka, A. Z. HrynkiewiczRequires cookie*
 Title    Electric Field Gradients at the In Site in Au-In Compounds  
 Abstract    The quadrupole interaction in Au-In compounds of different stoichiometrics was studied with the perturbed angular correlation technique. The electric field gradients at 11 : Cd probes were measured and the temperature dependences of the quadrupole frequencies were determined. A new high temperature phase of Auln above 630 K and a new metastable modification of Au 7 In 3 were found. 
  Reference    Z. Naturforsch. 53a, 349—354 (1998); received October 31 1997 
  Published    1998 
  Keywords    Perturbed Angular Correlations, EFG, Intermetallic Compounds, Au-In System 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0349.pdf 
 Identifier    ZNA-1998-53a-0349 
 Volume    53 
3Author    K. Królas, M. Rams, J. WojtkowskaRequires cookie*
 Title    Quadrupole Interaction of 172 Yb and 168 Er Nuclei in the First Excited 2 + State  
 Abstract    We have measured the hyperfine interactions in YbVC>4 and YbPC>4 using 172 Yb perturbed angular correlation spectroscopy for 90 -1094 keV and 1094 -79 keV 7-7 cascades. The quadrupole interaction frequency varied with temperature from 0 to 2 GHz. Precise information was obtained from both cascades independently even using the cascade with the intermediate state of the half life as short as 1.6 ns. 
  Reference    Z. Naturforsch. 55a, 45—18 (2000); received September 11 1999 
  Published    2000 
  Keywords    Quadrupole Interaction, Perturbed Angular Correlations, 172 Yb, 16X Er, YbVCV 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0045.pdf 
 Identifier    ZNA-2000-55a-0045 
 Volume    55 
4Author    Michael Uhrmacher, Klaus-Peter LiebRequires cookie*
 Title    Phase Transitions in Oxides Studied by Perturbed Angular Correlation Spectroscopy  
 Abstract    Radioactive atoms located on cation sites in oxide matrices can be used to monitor phase transitions by measuring the electric or magnetic hyperfine interactions by means of Perturbed Angular Correlations spectroscopy. The article illustrates three types of phase transitions studied with 11 'in tracers and their daughter nuclei m Cd, namely magnetic, structural and REDOX phase transitions in binary and ternary polycrystalline or single-crystalline oxides. In this context, we also discuss the question of identifying the probes' lattice site(s), the scaling of the Electric Field Gradients in oxides, the influence of the (impurity) probes themselves on the phase transitions, and the occurrence and mechanisms of dynamic interactions. Recent results on " 1 In in pure and Li-doped In 2 S 3 will also be presented. 
  Reference    Z. Naturforsch. 55a, 90—104 (2000); received August 26 1999 
  Published    2000 
  Keywords    Phase Transitions, Oxides, Perturbed Angular Correlations, 111 In, Point Charge Model 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0090.pdf 
 Identifier    ZNA-2000-55a-0090 
 Volume    55 
5Author    P. De, La Presa, K. P. Lieb, M. Uhrmacher, L. ZiegelerRequires cookie*
 Title    Perturbed Angular Correlation Studies in SrTi0 3 Single Crystals  
 Abstract    The quadrupole hyperfine interactions of 11 'Cd/ 111 In probe nuclei in single-crystalline SrTi0 3 perovskite samples were investigated using Perturbed Angular Correlation spectroscopy. Three electric field gradients were detected and their fractions and hyperfine parameters were measured in the temperature range from 26 to 700 K. The fraction / 0 having a vanishing quadrupole frequency, as expected for 111 Cd on substitutional sites in a cubic lattice, starts to develop around 300 K and reaches 100% at 700 K. Two well-defined EFG's having closely lying quadrupole frequencies and asymmetry parameters of cj qi = 49.1(3) Mrad/s, 77, = 0.10(2) and u Q2 = 51.8(3) Mrad/s, r] 2 = 0.12(2), at room temperature, were identified in the temperature range from 250 to 530 K, and their (100) orientation in the lattice was determined. They are associated with electronic defects at the probe atoms. 
  Reference    Z. Naturforsch. 55a, 237—241 (2000); received August 24 1999 
  Published    2000 
  Keywords    Perturbed Angular Correlations, SrTi0 3, Single Crystal, Electronic Defects, Perovskite 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0237.pdf 
 Identifier    ZNA-2000-55a-0237 
 Volume    55 
6Author    J. Roth, M. Uhrmacher, R. De, La Presa, L. Ziegeler, K. P. LiebRequires cookie*
 Title    Structural Phase Transitions in BaTi0 3 Studied via Perturbed Angular Correlations  
 Abstract    Phase transitions in the ferroelectric perovskite BaTi0 3 were studied for 111 In-implanted poly-crystalline samples by measuring the electric field gradients by means of Perturbed Angular Correla-tion spectroscopy. The phase transitions between the orthorhombic rhombohedral tetragonal cubic lattices were investigated in 2 -10 K steps, for increasing and decreasing temperatures, in order to determine their hysteresis. The transition parameters are compared with results from measurements of the spontaneous polarization, electric susceptibility and neutron scattering. 
  Reference    Z. Naturforsch. 55a, 242—246 (2000); received August 24 1999 
  Published    2000 
  Keywords    Perturbed Angular Correlations, BaTi0 3, Phase Transitions, Hysteresis, 1 " In 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0242.pdf 
 Identifier    ZNA-2000-55a-0242 
 Volume    55 
7Author    P. Wodniecki, B. Wodniecka, M. Marszalek, A. Z. HrynkiewiczRequires cookie*
 Title    PAC Studies of Ag-Hf Intermetallic Compounds  
 Abstract    The hyperfine quadrupole interaction of 181 Ta and 111 Cd probes in HfAg and HfiAg com-pounds was studied at 24 to 1100 K with the time -differential perturbed angular correlation (TDPAC) technique. The EFGs measured in HfAg on 181 Ta and m Cd are 1.388(5)x 10 18 VcnT 2 and 0.340(5)x 10 lx Vcm -2 , respectively. For both probe atoms a linear decrease of the EFG with temperature was observed with slopes 1.1 l(2)x 10 -4 KT 1 and 1.73(5)x 10~ 4 KT 1 for 181 Ta and "'Cd, respectively. In Hf 2 Ag, 0.469(2)x 10 18 VcnT 2 was determined on 181 Ta nuclei and 0.428(5)x 10 18 Vcm -2 on '"Cd. Also a linear EFG temperature dependence with the large slope of 2.39(6)x 10 -4 K" 1 was observed for "'Cd probes in Hf 2 Ag, while the EFG measured on l8l Ta nuclei in this compound exhibits a very weak temperature variation which can be fitted neither with a linear T nor a T ?/2 dependence. In all cases the electronic contributions to the EFG are very small indicating that these transition element systems do not obey the universal correlation between the electronic and the ionic EFG observed in numerous other systems not belonging to the transition metal series. 
  Reference    Z. Naturforsch. 51a, 437—441 (1996); received November 20 1995 
  Published    1996 
  Keywords    Hyperfine interactions, perturbed angular correlations, electric field gradient, inter-metallic compounds, Ag-Hf system 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0437.pdf 
 Identifier    ZNA-1996-51a-0437 
 Volume    51 
8Author    P. Wodniecki, B. Wodniecka, A. Kulińska, A. Z. HrynkiewiczRequires cookie*
 Title    Electric Quadrupole Interaction at 181 Ta in Isostructural Orthorhombic Cu 8 Hf 3 and Cu 8 Zr 3 Compounds  
 Abstract    The quadrupole interaction of 181 Ta probes in isostructural Cu 8 Hf 3 and Cu 8 Zr 3 intermetallic compounds was studied in the temperature range 24 K -1100 K with the time-differential perturbed angular correlation technique. Two nonaxial electric field gradients corresponding to two nonequiv-alent hafnium or zirconium sites in the investigated structure were found. A linear decrease in the quadrupole interaction frequency with increase of temperature for the 8(d) sites was evidenced, while the v Q (T) dependence for the 4(c) sites is weaker and has a T 312 character. 
  Reference    Z. Naturforsch. 53a, 355—357 (1998); received October 31 1997 
  Published    1998 
  Keywords    Hyperfine Interactions, Perturbed Angular Correlations, EFG, Intermetallic Compounds, Cu-Hf and Cu-Zr Systems 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0355.pdf 
 Identifier    ZNA-1998-53a-0355 
 Volume    53 
9Author    M. Dietrich, A. Burchard, D. Degering, M. Deicher, J. Kortus, R. Magerle, A. Möller, V. Samokhvalov, S. Unterricker, R. ViandenRequires cookie*
 Title    Quadrupole Interaction in Ternary Chalcopyrite Semiconductors: Experiments and Theory  
 Abstract    Electric field gradients have been measured at substitutional lattice sites in ternary semiconduc-tors using Perturbed 7-7 Angular Correlation spectroscopy (PAC). The experimental results for A I B III C 2 chalcopyrite structure compounds and • A 1I B2 C4 1 defect chalcopyrites are compared with ab-initio calculations. The latter were carried out with the WIEN code that uses the Full Poten-tial Linearized Augmented Plane Wave method within a density functional theory. The agreement between experiment and theory is in most cases very good. Furthermore, the anion displacements in AgGaX 2 -compounds (X: S, Se, Te) have been determined theoretically by determining the minimum of the total energy of the electrons in an elementary cell. 
  Reference    Z. Naturforsch. 55a, 256—260 (2000); received September 11 1999 
  Published    2000 
  Keywords    Quadrupole Interaction, Chalcopyrite Semiconductors, First Principles Calculations, Perturbed Angular Correlations, Structure Parameters 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0256.pdf 
 Identifier    ZNA-2000-55a-0256 
 Volume    55 
10Author    M. Rentería, L. A. Errico, A. G. Bibiloni, K. Freitag, F. G. RequejoRequires cookie*
 Title    PAC Identification of Electric-Nuclear-Quadrupole Interactions in Sm-Sesquioxides  
 Abstract    We present Perturbed Angular Correlation (PAC) results of the electric-nuclear quadrupole interaction at lxl Ta located at the nonequivalent cation sites of cubic C-Sm 2 0 3 and monoclinic B-Sm 2 0 3 free of defects. The application of the empirical Cd/Ta correlation found in binary oxides allowed us to correlate the interactions with each site and to identify the single Sm site populated in 111 In-implanted B-Sm 2 0 3 experiments. The preferential site occupation of Cd and Ta in B-Samaria is discussed in terms of the "chemistry" of the probe-atoms. 
  Reference    Z. Naturforsch. 55a, 155—159 (2000); received August 26 1999 
  Published    2000 
  Keywords    Perturbed-Angular Correlations, Electric-Field Gradients, Sm 2 0 3, Rare-earth Semiconductor and Insulator Oxides, lxl Hf-Impurity Implantation 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0155.pdf 
 Identifier    ZNA-2000-55a-0155 
 Volume    55