Non-pair forces and lattice dynamical properties of hexagonal close-packed lattice

1978 ◽  
Vol 56 (1) ◽  
pp. 63-67 ◽  
Author(s):  
S. K. Mishra ◽  
S. S. Kushwaha
Keyword(s):  
Specific Heat ◽  
Phonon Dispersion ◽  
Axial Ratio ◽  
Experimental Results ◽  
Hexagonal Close Packed ◽  
Dynamical Properties ◽  
Hcp Structure ◽  
Good Agreement ◽  
Phonon Dispersion Relations ◽  
The Ideal

Cadmium is a highly anisotropic hcp metal like zinc. It has an axial ratio (c/a = 1.8855) that is much higher than the ideal axial ratio for the hcp structure. The successful study of the lattice dynamical properties of Zn and Tl by the modified Cheveau model has created an interest in studying the phonon dispersion relations and specific heat of cadmium. The computed results are in reasonably good agreement with the experimental results.

Mechanical and thermodynamic properties of AlX (X = N, P, As) compounds

2017 ◽  
Vol 31 (23) ◽  
pp. 1750167 ◽  
Author(s):  
Lifang Xu ◽  
Wei Bu
Keyword(s):  
Thermodynamic Properties ◽  
Specific Heat ◽  
Atomic Number ◽  
Phonon Dispersion ◽  
Theoretical Data ◽  
Constant Volume ◽  
Vibrational Entropy ◽  
Debye Temperatures ◽  
The Difference ◽  
Good Agreement

The Vickers hardness of various AlX (X = N, P, As) compound polymorphs were calculated with the bond resistance model. Thermodynamic properties, such as vibrational entropy, constant volume specific heat and Debye temperatures, were calculated using phonon dispersion relations and phonon density of states (DOS). The calculated values are in good agreement with the previous experimental and theoretical data. For the same structure of AlX (X = N, P, As) compounds, their hardness and Debye temperatures both decrease with the X atomic number. The wurtzite (wz) and zincblende (zb) structures of the same compounds AlX share an almost identical hardness, but have different Debye temperatures. The difference between wz and zb structures increases as the atomic number of X increases. The thermodynamic properties reveal that the constant volume specific heat approaches the Dulong–Petit rule at high temperatures.

Lattice Dynamical Properties of Potassium

1981 ◽  
Vol 36 (11) ◽  
pp. 1242-1245
Author(s):  
O. P. Gupta
Keyword(s):  
Equilibrium Condition ◽  
Short Range ◽  
Phonon Dispersion ◽  
Waller Factor ◽  
Crystal Stability ◽  
Debye Waller Factor ◽  
Dynamical Properties ◽  
Experimental Values ◽  
Theoretical Results ◽  
Good Agreement

The phonon dispersion, temperature dependence of the Debye temperature, Debye-Waller factor, and Grüneisen parameter of potassium are calculated using a realistic lattice dynamical model. The model considers short range pairwise forces effective upto second neighbors and an improved electron ion interaction on the lines of Bhatia. An equilibrium condition, which preserves the crystal stability, is obtained. The theoretical results are found to be in good agreement with the experimental values.

scholarly journals INTERATOMIC FORCES, PHONONS, THE FOREMAN–LOMER THEOREM AND THE BLACKMAN SUM RULE

2001 ◽  
Vol 15 (26) ◽  
pp. 3439-3452 ◽  
Author(s):  
A. M. STEWART
Keyword(s):  
Phonon Dispersion ◽  
Dispersion Relations ◽  
Force Constants ◽  
Sum Rule ◽  
Cubic Crystals ◽  
Hexagonal Close Packed ◽  
Atomic Force ◽  
Principal Directions ◽  
General Relations ◽  
Phonon Dispersion Relations

Foreman and Lomer proposed in 1957 a method of estimating the harmonic forces between parallel planes of atoms of primitive cubic crystals by Fourier transforming the squared frequencies of phonons propagating along principal directions. A generalized form of this theorem is derived in this paper and it is shown that it is more appropriate to apply the method to certain combinations of the phonon dispersion relations rather than to individual dispersion relations themselves. Further, it is also shown how the method may be extended to the hexagonal close packed and diamond lattices. Explicit, exact and general relations in terms of atomic force constants are found for deviations from the Blackman sum rule which itself is shown to be derived from the generalized Foreman–Lomer theorem.

scholarly journals Phonon Dispersion Relations for Chromium and Tantalum

1975 ◽  
Vol 28 (1) ◽  
pp. 57 ◽  
Author(s):  
Jyoti Prakash ◽  
LP Pathak ◽  
MP Hemkar
Keyword(s):  
Force Constant ◽  
Phonon Dispersion ◽  
Normal Modes ◽  
Inelastic Neutron ◽  
Neutron Spectroscopy ◽  
Phonon Dispersion Curves ◽  
Modes Of Vibration ◽  
Experimental Values ◽  
Good Agreement ◽  
Phonon Dispersion Relations

Phonon dispersion curves for the normal modes of vibration in chromium and tantalum are calculated along the symmetry directions [100], [110] and [111] using the five force-constant model of Behari and Tripathi (1970a). The results are compared with experimental values obtained from inelastic neutron spectroscopy and reasonably good agreement is found.

INVESTIGATION OF THE ENTROPY AND SPECIFIC HEAT CAPACITY OF GaN USING INCOMPLETE GAMMA FUNCTIONS

2008 ◽  
Vol 22 (30) ◽  
pp. 5349-5355 ◽  
Author(s):  
SAVAŞ SÖNMEZOǦLU
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Experimental Results ◽  
Analytical Relation ◽  
Gamma Functions ◽  
Temperature Range ◽  
Incomplete Gamma Functions ◽  
Theoretical Results ◽  
Good Agreement

The aim of this paper is to provide validity and reliable analytical relation for the thermodynamic functions calculated in terms of the Debye temperature using incomplete gamma functions, and examines the entropy and specific heat capacity of hexagonal single crystals of GaN in the 0–1800 K temperature range. The obtained results have been compared with the corresponding experimental and theoretical results. Our results are in excellent agreement with the theoretical results over the entire temperature range. It has also shown that at low temperature, our results are in very good agreement with the experimental results, however, at high temperature, our results are lower than other experimental results.

Lattice dynamical study of face centred tetragonal indium

1983 ◽  
Vol 61 (1) ◽  
pp. 58-66 ◽  
Author(s):  
V. Ramamurthy ◽  
S. B. Rajendraprasad
Keyword(s):  
Frequency Distribution ◽  
Phonon Frequency ◽  
Phonon Dispersion ◽  
Dynamical Study ◽  
Atomic Interactions ◽  
Characteristic Features ◽  
Experimental Values ◽  
First Time ◽  
Good Agreement ◽  
Phonon Dispersion Relations

The phonon dispersion relations and the phonon frequency distribution function of fct indium have been deduced, for the first time, using a lattice dynamical model which expresses the atomic interactions in terms of central, angular, and volume forces. Six elastic constants, four zone boundary frequencies, and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and conforms with the translational symmetry of the lattice; the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, but disagree with the theoretical values of Chulkov et al. as well as those of Gunton and Saunders at several wave vectors and polarizations. In addition the phonon frequency distribution curve obtained from this model is in overall agreement with those obtained from the electron tunnelling data, the inelastic scattering of neutrons as well as a pseudopotential model. The apparent characteristic features of these curves, the implications of the crystallographic equivalence between fct and bet lattices, and their relevance in the lattice dynamical study of indium are discussed.

scholarly journals Dual-Frequency Circularly Polarized Truncated Square Aperture Patch Antenna with Slant Strip and L-Shaped Slot for WLAN Applications

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Sorana Niyamanon ◽  
Rewat Senathong ◽  
Chuwong Phongcharoenpanich
Keyword(s):  
Radiation Pattern ◽  
Patch Antenna ◽  
Axial Ratio ◽  
Experimental Results ◽  
Antenna Design ◽  
Impedance Bandwidth ◽  
Dual Frequency ◽  
Circularly Polarized ◽  
Good Agreement

This research proposes a dual-frequency circularly polarized truncated square aperture patch antenna with slant stripline and L-shaped slot for WLAN applications. In the antenna design, the parameters were optimized and the WLAN-enabled dual-frequency (2.4 and 5.8 GHz) antenna was realized. Simulations were subsequently carried out for the impedance bandwidth (S11) < −10 dB, axial ratio (AR) ≤ 3 dB, optimal gain, and bidirectional radiation pattern. To validate, an antenna prototype was fabricated and the experiments were undertaken. The simulated and experimental results are in good agreement. In essence, the proposed WLAN-enabled dual-frequency circularly polarized antenna is most suited for applications in the vertically and horizontally elongated areas, including in the tunnel, train carriage, and buildings.

scholarly journals A Liquid Metal Conical Helical Antenna for Circular Polarization-Reconfigurable Antenna

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Yun Zhou ◽  
Shaojun Fang ◽  
Hongmei Liu ◽  
Shiqiang Fu
Keyword(s):  
Liquid Metal ◽  
Circular Polarization ◽  
Pitch Angle ◽  
Axial Ratio ◽  
Experimental Results ◽  
Reconfigurable Antenna ◽  
Polarization Mode ◽  
Helical Antenna ◽  
Left Hand ◽  
Good Agreement

A novel polarization-reconfigurable conical helical antenna based on the liquid metal is presented. The antenna is implemented by using truncated structure, variable pitch angle, a matching stub, and a mechanical autorotation device. The experimental results show that a good agreement between simulations and measurements is obtained. The gain of the antenna achieves higher than 8 dBi in the work band (1525–1660.5 MHz), and the 3 dB axial ratio (AR) bandwidth reaches 410 MHz. The polarization mode of the antenna can be switched between right-hand and left-hand circular polarization.

Unpaired forces in the study of lattice dynamics of thorium

1979 ◽  
Vol 57 (11) ◽  
pp. 1838-1842 ◽  
Author(s):  
K. N. Awasthi ◽  
S. S. Kushwaha
Keyword(s):  
Experimental Data ◽  
Phenomenological Model ◽  
Lattice Dynamics ◽  
Phonon Dispersion ◽  
Body Rotation ◽  
Symmetry Requirement ◽  
Screened Coulomb Potential ◽  
Three Body ◽  
Good Agreement ◽  
Phonon Dispersion Relations

A phenomenological model that considers interaction between ions in terms of two-body (central) and three-body (unpaired) forces and evaluates the effect of electron–ion interaction through a screened coulomb potential is developed for studying the lattice dynamics of thorium. The model satisfies the symmetry requirement of a lattice and fulfils the condition of invariance under rigid body rotation. Computed phonon dispersion relations and (θD – T) curve for thorium are in reasonably good agreement with the corresponding experimental data.

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