The hydrostatic pressure derivatives of the elastic constants of indium and an indium cadmium alloy

The hydrostatic pressure derivatives of the elastic stiffness constants of indium and indium-3.4 at.% cadmium alloy single crystals have been obtained from pulse echo overlap measurements of the dependence of ultrasonic wave velocities upon pressure. The softest zone centre acoustic phonon mode in indium is a shear mode propagating k along the [101] direction rather than that (k[110], e[11?0]) which drives the ferroelastic phase transition in the indium-cadmium alloys. The derivative δ((C₁₁ – C₁₂)/2)/δP is positive, accounting for the stability of the fct structure of indium under high pressure. Using the quasiharmonic, anisotropic continuum model the acoustic mode Grüneisen parameters have been calculated and are discussed in terms of mode softening. The high temperature limiting value$\text{\$}\text{?}$γ_H (= 2.56) of the mean acoustic mode Grüneisen parameter is found to be close to the thermodynamic Grüneisen parameter γ^th (=2.5).     

The second Grüneisen constant of CsCl and CsI

The first order volume dependence of the Grüneisen constant, commonly known as the second Grüneisen constant, has been obtained in a quasi-harmonic approximation as a function of temperature for CsCl and CsI. The calculations are performed using a volume dependent modified rigid ion model of lattice dynamics. The variation of the microscopic second mode-Grüneisen parameter as a function of wave vector in various directions of high symmetry is also calculated. The theoretically calculated second Grüneisen constants are compared to the values calculated using available thermodynamic data.     

室温下金属中电子格林艾森常数的测量

在室温条件下用自己研制的超快电子衍射实验设备精确测量了金属铝的电子格林艾森常数(γ_e).当飞秒脉冲激光瞬间加热铝膜时,电子和晶格对固体热膨胀的作用在时间域上是不同步的,借助于超快电子衍射实验设备的高时间分辨能力,可以摆脱以往测量非磁性金属材料时低温的限制,在室温条件下,实验通过直接观测瞬间加热的铝膜中电子和晶格对热膨胀的不同贡献得到电子的格林艾森常数. 关键词： 格林艾森常数 超快电子衍射 晶格热运动 电子热运动     

Anomalous shape of cyclotron resonance line in n-GaP in high magnetic fields

Cyclotron resonance in n-GaP has been observed at 119 μm in pulsed magnetic fields up to 410 kG. From the experiments with the magnetic field parallel to the 〈100〉, 〈110〉 and 〈111〉 axes, it is concluded that the transverse effective mass for electron is and that the anisotropy factor of the conduction band is K = 7.9^+3.2_?2.0. An anomalous shape of the absorption curve was found in the magnetic field directions parallel to the crystal axes 〈110〉 and 〈111〉.     

keV Neutron capture cross sections of 134Ba and 136Ba

The neutron capture cross sections of ¹³⁴Ba and ¹³⁶Ba have been measured in the energy region 3 to ¹⁰⁰keV. The following average quantities were deduced from the extracted resonance parameters: 〈D〉 = 127±10eV, 10⁴S₀ = 0.85±0.3, 10⁴S₁ = 0.8, 〈Γ_γ〉 = 120±20 meV for ¹³⁴Ba. Analysis of the ¹³⁶Ba data gave 〈Γ_γ〉 = 125±30meV for s-wave neutrons. The average 30 keV capture cross sections for these two s-process nuclei were found to be $\text{225±35}\text{mb}\text{for}{}^{134}\text{Ba and}\text{61±10}\text{mb}\text{for}{}^{136}\text{Ba}$.     

Grüneisen parameter of NaCl at high compressions

A new method of determining the pressure dependence of the Grüneisen parameter is described. The measurements were carried out on NaCl to 33 kbar at room temperature using an end-loaded piston-cylinder apparatus. A fluid cell arrangement with Bridgman unsupported area seals was used. Changes of sample temperature associated with small adiabatic pressure changes were measured and the Grüneisen parameter could be calculated from the thermodynamic relationship $\text{γ = (}\text{K}{}_{\mathrm{s}}\text{T}\text{)(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}$ where K_s is the adiabatic bulk modulus. Our results are in excellent agreement with those reported by Roberts and Ruppin [1] who calculated the pressure dependence of γ from thermodynamic and ultrasonic data and in excellent agreement with those reported by Hardy and Karo [2] who carried out a lattice-dynamical calculation.     

Pressure derivatives of the elastic moduli of strontium,barium and lead nitrate

The pressure derivatives of the elastic moduli of Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ single crystal, have been measured by the ultrasonic pulse superposition method. The results for Sr(NO₃)₂ and Pb(NO₃)₂ are similar in magnitude and character, while the ones for Ba(NO₃)₂ differ strongly, $\text{?c}{}_{11}\text{?P}$ and $\text{?c}{}_{12}\text{?P}$ even From the measured pressure derivatives, the mode Grüneisen gammas and the Grüneisen constant as a function of temperature have been determined, and the latter is correlated with the experimental values, deduced from thermal expansion. The explicit temperature dependence of the elastic moduli is calculated, and found to be always negative, increasing in absolute value from Sr(NO₃)₂ to Pb(NO₃)₂.     

Raman and mid-infrared spectroscopic study of the phase transitions in octafluoronaphthalene at elevated pressures

Raman and mid-infrared spectra of C₁₀F₈ have been obtained under hydrostatic pressures up to 17 kbar in a diamond anvil cell. The C₁₀F₈ I–II phase change, previously observed by neutron diffraction at about 0.8 kbar, has been confirmed. No evidence was found to support the existence of a furtt ier phase change between 4 and 6 kbar indicated by the neutron work, although this is certainly not precluded as the extra spectral features expected in this case are extremely small. The mode Grüneisen parameters, γ_i, allow a clear distinction between internal and external molecular modes, and scale roughly in accord with Zallen's relation γ_i$\text{\$}\text{?}$v_i^?2.     

Baryon mass splitting by the strong hyperfine interaction and SU(3) breaking

We calculate mass splittings of strange and non-strange baryons in the [56, 0⁺] and the [70, 1^?]. As the most important spin-dependent force we only analyse the hyperfine interaction. The exact treatment of the quark mass breaking shows contributions which have not been considered in similar investigations up to now. Taking $\text{mλ}\text{m}{}_{\mathrm{<mtext>p</mtext>}}\text{? 2}$ and popular values for the slope of the linear potential a, the strong coupling constant α_s and the p-quark mass, we get excellent results for the four mass splittings 〈Σ-Λ〉, $\text{〈Σ}{}^1\text{? Σ〉}$, 〈Δ-N〉 and $\text{〈Ξ}{}^1\text{? Ξ〉}$ in the [56, 0⁺]. The structure of mass spectrum in the [70, 1^?] is well described, too; the strong SU(3) mixing of Σ and Λ states is seen to be due to the quark mass breaking. Predictions for missing Σ states in the [70, 1^?] as as for splittings between charmed baryons can be made.     

A new expression for the Anderson-Grüneisen parameter δ for ionic crystals

The Anderson-Grüneisen parameter δ has been computed theoretically from a general expression developed by Sharma and Tripathi[6]. The δ-γ (Grüneisen parameter) curves have been plotted to find a relation for the best fitted yielding curves by the method of least squares. The relation developed can be put as δ = AγB and it can be inferred that chang's[3] relation is a particular case of this general equation.     

Low temperature magnetostriction studies in CsNiCl3

The forced magnetostriction of the linear-chain antiferromagnet CsNiCl₃ has been measured from 1.6 to 20K. For the applied field parallel to the c-axis the data below the Néel temperature T_N clearly show the effects of the spin-flop near 20 kG. Effects ascribed to domain realignment are observed below 5 kG for the field normal to the c-axis. In the paramagnetic phase above T_N the magnetostrictive behavior conforms to a simple model in which the intrachain exchange J is a function only of the c-parameter. The resulting partial Grüneisen parameter $\text{γ∥}{}^{\mathrm{m}}\text{=}\text{?d(?nJ)}\text{d(?nc)}$ is compared with that obtained from thermal expansion measurements.     

Search for parity-nonconservation effects in deep-inelastic μ-N interaction

The difference of the cross sections for deep inelastic scattering of muons with average momenta 21 GeV/c with right and left helicity at large angles, i.e., with large momentum transfer, has been measured. No statistically-significant dependence of cross sections on the longitudinal polarization of muons has been found, i.e. no parity-nonconservation effects in deep inelastic μN interaction have been observed. The magnitude of the cross-section asymmetry $\text{R =}\text{[〈σ}{}_{\mathrm{<mtext>R</mtext>}}\text{〉 ? 〈σ}{}_{\mathrm{<mtext>L</mtext>}}\text{〉]}\text{[〈σ}{}_{\mathrm{<mtext>R</mtext>}}\text{〉+ + 〈σ}{}_{\mathrm{<mtext>L</mtext>}}\text{〉]}$ may be represented as R = β〈Q²〉 = (? 4 ± 6) × 10^?3 〈Q², (GeV/c)²〉. The limitations G_o^(μ) = (+ 6 ± 10)G have been obtained for the constant G_o^(μ) of vector-axial interaction $\text{(}\text{G}{}_{\mathrm{<mtext>o</mtext>}}{}^{\mathrm{(\mu )}}\text{2}\text{) [}\text{μ}\text{γα(1 + γ}{}_5\text{)μ] J}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>o</mtext>}}$ (hadron, V-A).     

The Grüneisen parameter γ of KBr,RbCl and Bi through high pressure phase transitions

High pressure values for the adiabatic pressure derivative of temperature $\text{(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}$ have been obtained by measuring the temperature change caused by a small rapid increase in pressure. Values for KBr and RbCl in phases B1 and B2 and for Bi in phases I, II and III are given for T = 295 K. The Grüneisen parameter γ is given by $\text{γ =}\text{B}{}_{\mathrm{s}}\text{(}\text{?T}\text{?P}\text{)}{}_{\mathrm{s}}\text{T}$ where B_s is the adiabatic bulk modulus. Ultrasonic and statk compressibility data are used to estimate the pressure and phase dependence of B_s. Dramatic increases in both γ and (?T/?P)_s are observed as the pressure increases through a phase transition. Values for the logarithmic derivate $\text{q ≡ (? ln}\text{γ}\text{?}\text{ln V}{}_{\mathrm{T}}$ are given.     

Lattice dynamical calculation of the second Grüneisen constant of CsBr

The second order Grüneisen constant constitutes an additional measure of the anharmonicity in a solid (the Grüneisen constant itself being the first measure). This quantity and the corresponding second mode-Grüneisen parameters are calculated for CsBr using a modified rigid ion model of lattice dynamics. The model parameters are deduced from the three elastic constants and the long wavelength optical mode frequencies. Using the first and second order pressure dependences of these physical observables, the individual second mode-Grüneisen parameters are obtained as a function of wave vector. The temperature variation of the second Grüneisen constant is then deduced in a quasi-harmonic approximation. The second Grüneisen constant is also calculated from available thermodynamic data and is in reasonable agreement with the present theoretical prediction.     

Impurity lattice dynamics of Fe in Cr from precision Mössbauer fraction measurements

Precision 〈x²〉-values and their anharmonicity been measured for ⁵⁷Fe in Cr between 80 K and 600 K. At 294 K. $\text{? = 0.798 ± 0.005}$. A theoretical analysis based upon Cr neutron scattering data yields 0.8 for the impurity/host force constant ratio.     

The Glimm-Jaffe-Spencer expansion for the classical boundary conditions and coexistence of phases in the λφ24 Euclidean (quantum) field theory

The λφ₂⁴ Euclidean (quantum) field theory is studied in the multiphase region, and the following results are proven: (1) The “low temperature” expansion converges for Dirichlet (D), free (F), Neumann (N), and periodic (P), boundary conditions, and the even-point Schwinger functions for these boundary conditions have a mass gap; (2) $\text{〈}\text{o}\text{〉}{}^{\mathrm{b}}\text{=}\text{1}\text{2}\text{〈o〉}{}^{\mathrm{+}}\text{+}\text{1}\text{2}\text{〈o〉}{}^{\mathrm{?}}$, where b = D, F, N, P, and 〈o〉^± are the pure states of Glimm, Jaffe, and Spencer; (3) 〈o〉^±ξ = 〈o〉^± for all ξ > 0, where ξ is the buondary field; (4) alternative characterizations of the pure states 〈·〉^± are given.     

S-P wave interference in K+K− photoproduction near K+K− threshold

A mass-dependent asymmetry was observed in the decay angular distribution of a photoproduced K⁺K^? system near the K⁺K^? threshold. The corresponding moments 〈Y₁⁰〉 have been evaluated. Interpreting the asymmetry as an S-P wave interface due to the states S₉₉₃¹(0⁺) and ø₁₀₁₉(1^?) one can compute the moments 〈Y₁⁰〉 through an amplitude analysis. The theoretical calculation reproduces the experimental results well, if one assumes a real S-wave amplitude for the S₉₉₃¹. The data cannot be explained by a non-resonant real S-wave. Other possibilities have been discussed. An estimate of the photoproduction cross section of the $\text{S}{}^1\text{→}\text{K}{}^{\mathrm{+}}\text{K}{}^{\mathrm{?}}$ can be given on the basis of the above hypothesis.     

Thermal expansion and mode Grüneisen parameters of LiH and LiD

The third order contribution of the shell-shell interaction between next nearest neighbours has been determined from a calculation of the coefficient of linear thermal expansion of LiH and ⁷LiD. The Coulomb anharmonicity is included. A shell model fitted to phonon energies from inelastic neutron scattering in ⁷LiD was used. From this model then averaged Grüneisen constants and individual mode Grüneisen parameters have been deduced.