بررسی خواص ترمودینامیکی و ارتعاشی ThC تحت فشار و دمای بالا

نوع مقاله : مقاله پژوهشی کامل

نویسندگان

گروه فیزیک، دانشکده علوم پایه، دانشگاه مازندران، بابلسر، ایران

چکیده

در این تحقیق، خواص ساختاری، ترمودینامیکی و پاشندگی فونونی کاربید توریم توسط نظریۀ تابعی چگالی و نظریۀ اختلالی تابعی چگالی با استفاده از محاسبات ابتدا به ساکن در چارچوب روش امواج تخت مورد بررسی قرار گرفته است. از شبه پتانسیل‌های فوق نرم با تابعیت تقریب شیب تعمیم یافته برای پتانسیل تبادلی و همبستگی استفاده شده است. خواص ترمودینامیکیِ کاربید توریم تحت مدل شبه هماهنگ دبای – گرونیسن همان‌طور که در کد GIBBS2 پیاده‌سازی شده برای اولین بار مورد بررسی قرار گرفته است. خواص ساختاری شامل ثابت شبکه (a0)، مدول حجمی (B0) و مشتق مرتبه اول مدول حجمی (B0') با برازش معادله حالت درجه سوم بریچ – مورناگون محاسبه و با سایر کارهای نظری و تجربی مقایسه شدند که سازگاری خوبی با یکدیگر داشتند. ساختار نوار فونونی توسط نظریۀ اختلالی تابعی چگالی برای ثابت شبکۀ محاسبه شده و تجربی مورد بررسی قرار گرفت و گپ فونونی بدست آمده در حدود cm-1185 بود. مشاهده شد که دمای دبای با افزایش دما در یک فشار ثابت کاهش می‌یافت در حالی که با افزایش فشار برای تمام دماها افزایش می‌یافت. انرژی آزاد هلمهولتز ارتعاشی، انرژی آزاد گیبس، مدول حجمی آدیاباتیک، مدول حجمی همدما با افزایش دما در یک فشار ثابت کاهش پیدا می‌کردند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation of Vibrational and Thermodynamic Characteristics of ThC Under High Pressure and Temperature

نویسندگان [English]

  • Mohammad Hossein Sahafi
  • Mohammad Hossein Sahafi
Department of Physics, Faculty of Science, University of Mazandaran, Babolsar, Iran
چکیده [English]

In this paper, the structural, thermodynamic properties and phonon dispersion of thorium carbide are investigated through the density functional theory and the density-functional perturbation theory by using ab initio calculations within the framework of the plane-wave method. Ultrasoft pseudopotentials with GGA-PBE functional are utilized for the exchange and correlation potential. Thermodynamic properties of ThC are studied for the first time under the quasi-harmonic Debye-Gruneisen model as was implemented in the GIBBS2 code. Structural properties including lattice constant (a0), bulk modulus (B0) and the first derivative of the bulk modulus (B0') are calculated by fitting the third-order Birch-Murnaghan equation of state and compared to other theoretical and experimental works that revealed a good agreement. The phonon band structure is calculated from the density-functional perturbation theory for the lattice constant and investigated experimentally and the obtained phonon gap was about 185 cm-1. It was observed that the Debye temperature decreases with increasing the temperature at a constant pressure while it increases with increasing the pressure for all temperatures. The Vibrational Helmholtz free energy, the Gibbs free energy, the adiabatic bulk modulus, and the isothermal bulk modulus decreased with increasing the temperature at a given pressure.

کلیدواژه‌ها [English]

  • Debye-Gruneisen quasi-harmonic model
  • Thermodynamic properties
  • Gruneisen parameter
  • Phonon dispersion
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