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2D Nanomaterials for Flexible Supercapacitors
Published in Ram K. Gupta, Energy Applications of 2D Nanomaterials, 2022
Yamin Zhang, Jinyang Zhang, Linrui Hou, Changzhou Yuan
MXenes material is a kind of two-dimensional layered metal carbon/nitrogen compounds, which has been widely concerned for its excellent properties such as diversity of elemental composition, high electron mobility, unique in-plane anisotropy, high electrical conductivity, and excellent mechanical properties. The precursor phase of MXenes is MAX phase, where M is the transition metal element, A is the III or the IV main group element, and X is N or C. MXenes are usually obtained by the selective etching of a layer by MAX using hydrofluoric acid (HF), fluoric acid/hydrochloric acid mixture, and other methods [30]. In 2011, Prof. Gogotsi and Barsoum from Drexel University, USA, obtained Ti3C2 by hydrofluoric acid etching Al in Ti3AlC2 for the first time and named it MXenes. Up to now, 155 species of precursor MAX phase have been reported, and according to the theoretical prediction, more than 80 species of MXenes can be found, and a variety of solid solutions can be formed by changing the composition, so it can be predicted that MXenes will be a large family [31].
Ab Initio-Based Band Engineering and Rational Design of Thermoelectric Materials
Published in D. M. Rowe, Materials, Preparation, and Characterization in Thermoelectrics, 2017
Jiong Yang, Xun Shi, Wenqing Zhang, Lidong Chen, Jihui Yang
Figure 9.5 shows the crystal structure of a typical HH compound. There are three atomic positions, A, B, and X in one primitive unit cell. For TE HHs, A is usually an early transition (IIIB or IVB) or rare-earth metal, X is a main group element (IVA or VA), and B is normally a TM between A and X in the periodic table. The structural information of HH compounds in this work is mainly taken from the ICSD database which has more than 100 HH compounds. We used the following rules to select HHs for further detailed investigation. VEC equals to 18. Chemical bonding analysis showed that only HHs with 18 valence electrons may be semiconductors, which are suitable for TE purpose.The HH compounds with lanthanides, except for La, are not included. Lanthanides contained HHs usually have no gaps, behave as metals, and therefore possess poor TE properties. Besides, unfilled f electrons usually need to be treated by ab initio method with strong-correlation effects included.
2-Related 1–2–2 Zintl Phases
Published in Zhifeng Ren, Yucheng Lan, Qinyong Zhang, Advanced Thermoelectrics, 2017
For the layered AB2X2 Zintl phases crystallizing in CaAl2Si2-type structure (space group P3¯m1) reported as the TE candidates, the A site contains alkaline-earth or divalent rare-earth element such as Mg, Ca, Ba, Sr, Yb, and Eu; B is a d0, d5, d10 transition metal (e.g., Mn, Zn, and Cd) or a main group element such as Mg, while X comes from groups 14 and 15 such as Sb and Bi.14 Following the Zintl–Klemm concept, B and X form anionic sheets with covalent bonding due to the similar electronegativity, while A2+ cations donate electrons to the (B2X2)2− framework. The structure is often depicted as in Figure 7.1, clearly showing the bonding within the B–X layers between planes of A2+.
Investigations of martensitic, thermodynamics, elastic, electronic, magnetic, thermal and thermoelectric properties of Co2FeZ Heusler alloys (Z=Si; Ge; Al; Ga): a first principle study
Published in Molecular Physics, 2022
M. Y. Raïâ, R. Masrour, A. Jabar, M. Hamedoun, A. Rezzouk, A. Hourmatallah, N. Benzakour, K. Bouslykhane, J. Kharbach
Heusler compounds X2YZ are ternary intermetallic, where X and Y are transition metals and Z is the main group element. These type of compounds crystallised in the L21 crystal structure (space group: 225 Fm-3m) can be considered as a simple cubic lattice for X atoms; also the X and Y atoms are arranged at alternate body-centered positions. The X atoms are placed at (1/4,1/4, 1/4) and (3/4, 3/4, 3/4) sites, while Y and Z atoms are located on (0, 0, 0) and (1/2, 1/2, 1/2) sites in Wyckoff coordinates, respectively. In the Co2FeZ compound (with Z = Si, Ge, Al, Ga), each Fe or Z atom is surrounded by eight Co atoms, whereas each Co is surrounded by four Fe and four Z atoms. The L10 type tetragonal phase (space group: I4/mmm (139)) with formula Co4Fe2Z2, and Co, Fe and Z atoms occupy (1/2, 0, 1/4), (1/2, 1/2, 0) and (0, 0, 0) Wyckoff positions, respectively. The structure of Co2FeZ (Z = Cr, Fe, Co) compounds in both the L21 and L10 phases are displayed in Figure 1.
The effect of uniaxial stress on magneto-electronic properties and band Jahn–Teller distortion of Ni2MnGa Heusler alloy: an ab initio study
Published in Philosophical Magazine, 2022
El Habib Abbes, Hamza Abbassa, Said Meskine, Abdesamed Benbedra, Abdelkader Boukortt
The Heusler compounds with the chemical formula X2YZ [1–3] have attracted scientific and technological attentions due to their high potential as spintronic, thermoelectric [4,5] or shape-memory materials with various applications in the biomedical field because of their functional properties [6]. Chemically, they are formed by transition metals (X and Y) and the main group element (Z). They also crystallise in the cubic structure L21 (AlCu2Mn-type) with the space group . It results from four interpenetrating sub-lattices (fcc) [7] where X, Y and Z atoms are placed on the Wyckoff positions 8c (1/4, 1/4, 1/4), 4a (0, 0, 0) and 4b (1/2, 1/2, 1/2), respectively [8–10]. Another structure is frequently observed when the nuclear charge of the Y element is higher than the one of the X element (between two 3d transition metals). It is the cubic structure X (CuHg2Ti-type) with the space group with the chemical formula XYXZ, where X atoms occupy the non-equivalent 4a (0, 0, 0) and 4c (1/4,1/4, 1/4) positions, while Y and Z atoms are located on 4b (1/2, 1/2,1/2) and 4d (3/4, 3/4, 3/4) Wyckoff positions, respectively [11–13]. Half-Heusler alloys with the chemical formula XYZ are derived from the CuHg2Ti-type structure when 4d (3/4, 3/4, 3/4) is empty [4,5].
Structural, electronic, magnetic and thermoelectric properties of inverse Heusler alloys Ti2CoSi, Mn2CoAl and Cr2ZnSi by employing Ab initio calculations
Published in Philosophical Magazine, 2020
D. J. Mokhtari, Inshad Jum’h, H. Baaziz, Z. Charifi, T. Ghellab, Ahmad Telfah, Roland Hergenröder
In general, ternary Heusler alloys have two high ordered structures, namely, the classic Cu2MnAl-type structure and the newly discovered Hg2CuTi-type structure. The inverse Heusler alloys (Hg2CuTi) have composition X2YZ with space group. In Wyckoff positions, X is located at (0,0,0) and (1/4, 1/4, 1/4), Y and Z are located at (1/2, 1/2, 1/2) and (3/4, 3/4, 3/4) respectively [24]. X and Y denote a transition metal, while Z denotes a main group element (Figure 1(b)). Under ambient conditions, the inverse Heusler compounds Ti2CoSi, Mn2CoAl and Cr2ZnSi crystallises in the type Hg2CuTi structure (see Figure 2) and it is demonstrated that the later phase is the most stable. The high-pressure structure is Cu2MnAl type-structure with (225) space group. To find the favourable magnetic state of each alloy we calculated the total energy versus volume for the three magnetic states: the ferromagnetic (FM), Non-magnetic (NM) and antiferromagnetic (AFM) states.