A comparative ab initio study of the ferroelectric behaviour in KNO3 and CaCO3

Potassium nitrate exhibits a reentrant phase transformation, where a metastable ferroelectric phase (gamma-KNO3) is formed upon cooling from high temperature. The layered structure of this ferroelectric phase is composed of alternating layers of potassium ions and nitrate groups; wherein, a central nitrogen atom is coordinated by three equilateral triangular oxygen atoms. The group layer is located less than midway between the cation layers, giving rise to a polar structure. From a structural perspective, the calcite phase of calcium carbonate looks quite similar to this ferroelectric phase; however; it does not exhibit a ferroelectric transition. In this work we have performed an ab initio computational analysis to study the: structural stability, electronic characteristics, and bonding of various phases and ferroelectric properties of CaCO3 and KNO3. We find that both material systems have mixed covalent and ionic bonding. The covalent interactions are within the group atoms of carbonate and nitrate atoms while the ionic interactions occur between the negatively charged ( carbonate or nitrate) group and the calcium or potassium cations. For the low temperature stable phase of CaCO3 (calcite), however, there is a slight covalency between the cations and the oxygen atoms of the group. This latter interaction results in the crystallization of CaCO3 in the calcite form and prevents a ferroelectric transition. We suggest that, in analogy to KNO3, a metastable form of CaCO3 may also exist, similar to the phase of gamma-KNO3 that should have a spontaneous polarization equal to 30.6 mu C cm(-2), twice that of gamma-KNO3. Moreover, our analysis indicates that this material should have a coercive field smaller than that of gamma-KNO3.


A novel experimental and density functional theory study on palladium and nitrogen doped few layer graphene surface towards glucose adsorption and electrooxidation
Caglar, Aykut; Duzenli, Derya; Önal, Işık; Tezsevin, Ilker; Sahin, Ozlem; Demir Kıvrak, Hilal (Elsevier BV, 2021-03-01)
At present, few layer graphene (G) and nitrogen doped few layer graphene (N doped-G) are firstly coated on Cu foil via chemical vapor deposition (CVD) method and G and N doped-G coated Cu foil is transferred to the indium tin oxide (ITO) substrate surface to obtain electrodes. Pd metal is electrodeposited onto the N doped-G/ITO electrode (Pd-N doped-G/ITO). Pd-N doped-G/ITO electrode are characterized with advanced surface characterization methods such as Raman spectroscopy and SEM-EDX. Characterization res...
Comparison of the short and long-term degradation behaviors of as-cast pure Mg, AZ91 and WE43 alloys
Ocal, Ezgi Butev; ESEN, ZİYA; Aydınol, Mehmet Kadri; Dericioğlu, Arcan Fehmi (Elsevier BV, 2020-02-01)
The corrosion behaviors of pure magnesium, AZ91, and WE43 alloys have been evaluated by weight loss, hydrogen evolution rate, pH change measurements and potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS) methods. Main corrosion product formed on the surface of Mg/Mg-alloys after immersion of 24 h was Mg(OH)(2) on the other hand, at the end of the 20 days additional CaCO3 which was found to display a critical role in degradation characteristics of the samples, was found. Exa...
Analysis of the Specific Heat in the Supercooled Solid Phase of Liquid Crystals
Kilit, Emel; Yurtseven, Hasan Hamit (Informa UK Limited, 2011-01-01)
The specific heat Cp is analyzed using the experimental data at various temperatures in the solid phase of cholesteryl myristate according to a power-law formula for the rapidly and slowly cooled solid in the stability limit. We also analyze the temperature dependence of the Cp using the experimental data for the supercooled solid phase of p-azoxyanisole in the stability limit and the stability temperatures are determined for both cholesteryl myristate and p-azoxyanisole.
A study of phase stability and mechanical properties of hydroxylapatite-nanosize alpha-alumina composites
Evis, Zafer (Elsevier BV, 2007-04-01)
Hydroxylapatite (HA)-nanosize alumina composites were synthesized to study their phase stability and mechanical properties. To make these composites, nanosize alpha-Al2O3 powder was used because of its better sinterability and densification as compared to nanosize gamma-Al2O3. The composites were air sintered without pressure and hot pressed in vacuum at 1100 degrees C and 1200 degrees C. In the composites, HA decomposed to tricalcium phosphate faster after the air sintering than hot pressing. Moreover, hex...
Karakaş, Gürkan (Wiley, 1989-01-01)
Effects of concentration changes in initiator species Na2SO3, (NH4)2S2O8 and CuSO4, and emulsifier, ammonium stearate, on poly(vinyl chloride) (PVC) emulsion polymerization kinetics and on product particle size were experimentally investigated. It was observed that to obtain industrially significant rates and overall conversions, not only an optimum concentration ratio of Na2SO3/(NH4)2S2O8/CuSO 4 must be used, but also the concentrations of these species must be above certain limits. Increasing the concentr...
Citation Formats
M. K. Aydınol and S. P. Alpay, “A comparative ab initio study of the ferroelectric behaviour in KNO3 and CaCO3,” JOURNAL OF PHYSICS-CONDENSED MATTER, pp. 0–0, 2007, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/36910.