scholarly journals Nonlinear Effects in the Phonon System of Diamond Crystal

Thermodynamic properties of diamond are theoretically investigated on the ground of self-consistent description of a phonon gas in lattice, which generalizes the Debye model with taking into account the phonon-phonon interaction. In many cases properties of crystals of certain symmetry can be well approximated by a model of an isotropic continuous medium, if its elastic moduli are chosen optimally. They should be found for a crystal of each symmetry from the condition of their proximity to the exact elastic moduli, which are measured experimentally and are given in the corresponding tables. At high temperatures, the nonlinear phonon interaction takes into account both three- and four-phonon interactions. In this reason we take into account not only the second-order elastic moduli tensor in the reduced isotropic crystal model, but also the third- and fourth-order elastic moduli tensors, which are all together characterized by nine independent components. Account of the phonon-phonon interaction leads to the redefinition of the phonon’s speed and of the Debye energy. Their dependence on the temperature occurs. In the absence of interaction and neglecting the nonlinear effects, the phonons are the same as that of the Debye model. They are called "bare" or "Debye". Phonons whose speed is renormalized due to the interaction are called the “self-consistent” ones. It is shown that, at high temperatures, the theory predicts the linear in the temperature deviation of the isochoric heat capacity from the Dulong-Petit law. Unlike for the most crystals, where the decrease in the isochoric heat capacity is observed, our calculations for diamond and crystals with diamond structure predict the linear increase of the isochoric heat capacity with the temperature, viewed experimentally. The isobaric heat capacity of diamond, similar to other substances, linearly increases with the temperature.

1978 ◽  
Author(s):  
Richard A. Robie ◽  
B.S. Hemingway ◽  
C.M. Schafer ◽  
J.L. Haas

Author(s):  
Dinesh Varshney ◽  
Dinesh Choudhary

In this paper, we develop a theoretical model for quantitative analysis of temperature-dependent heat capacity calculation of the magnetoresistance compounds RMnO 3 ( R = La , Nd ). The results on heat capacity obtained by us are in good agreement with the measured values. An effective interionic interaction potential (EIoIP) with the long-range Coulomb, van der Waals (vdW) interaction and short-range repulsive interaction up to second neighbor ions within the Hafemeister and Flygare approach was formulated to estimate the Debye and Einstein temperature and was found to be consistent with the available experimental data. In addition, the properties studied are the cohesive energy, molecular force constant, Restrahlen frequency and Gruneisen parameter. After characterizing thermal properties, a systematic investigation of elastic behavior has been undertaken and it has been found that the elastic moduli are decreasing continuously with increasing temperature.


2010 ◽  
Vol 2010 (2) ◽  
pp. 146-149 ◽  
Author(s):  
V. I. Minchenko ◽  
I. V. Korzun ◽  
V. A. Khokhlov ◽  
V. N. Dokutovich

1959 ◽  
Vol 63 (9) ◽  
pp. 1505-1506 ◽  
Author(s):  
M. S. Chrasekharaiah ◽  
R. T. Grimley ◽  
John L. Margrave

Silicon ◽  
2018 ◽  
Vol 10 (5) ◽  
pp. 2307-2315
Author(s):  
Boussaid Olfa ◽  
Boussaid Ahlem ◽  
Fnaiech Mustapha

2021 ◽  
pp. 45-61
Author(s):  
I. Antypov ◽  
◽  
A. Mishchenko ◽  
O. Shelimanova ◽  
S. Tarasenko ◽  
...  

When assessing the thermal condition of the building and the parameters of the microclimate of the premises, the main factors influencing its thermal inertia were identified and taken into account. An assessment of the influence of the resistance of enclosing structures on the efficiency of the heating system, taking into account the influence of external and internal climatic parameters in the dynamic mode. It is shown that the time factor and depth of regulation, as well as the outdoor air temperature are important factors. Researches are carried out and the expediency of introduction of a duty mode of heating of buildings of HIGH SCHOOLS is estimated. The given algorithm of control of process of heat release (especially in the presence of a point of "breaking" - average (them) on the schedule) in addition increases accuracy of the decisions of the specified problems and reduces a temperature deviation by 4 ÷ 6 ° C in comparison with usual ("linear") dependence that allows to correct more precisely release of the heat carrier in system of heating of a structure at introduction of a standby mode. It was found that it took about 6.5 hours to achieve normalized air temperature and space heating in the forced (after a long stay on duty). It is shown that the heat consumption of the system in such conditions of its operation compared to the nominal mode increased by 25 % (taking into account the limit value of the specific allowance from table H1 DBN B.2.5-67: 2013 "Heating, ventilation and air conditioning"), but for the entire period the action of the standby mode savings amounted to about 6-8% of energy consumed. Taking into account the design of the outer walls of the object of study, the temperature graph of the heating system was adjusted taking into account the value of the internal heat capacity of the building when implementing on-duty heating, which, according to preliminary estimates, will: improve comfort in the room; to reduce heating costs of the educational and administrative building of NULES of Ukraine by 10-12 % for the heating period. Key words: microclimate, internal heat capacity of a building, standby mode, heating system, heat loss


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