First-Principles Thermoelectric Study of SrMgSi and CaMgGe Zintl-Phase Compounds

Zintl-phase semiconductor materials with low intrinsic lattice thermal conductivity have been the target of study for thermoelectric (TE) applications. Herein, we report Zintl-phase TiNiSi-type SrMgSi and CaMgGe with calculated low intrinsic lattice thermal conductivity (κL) values of 2.52 and 1.90 W/m·K at room temperature, respectively. The low κL is mainly due to the strong lattice anharmonicity, which originates from the weak bonding of cations in the anionic network, and strong optical-acoustic phonon coupling. Additionally, the high band degeneracy results in good electrical properties, and excellent ZT values of ∼2.83 (n-type, 500 K) and 3.09 (n-type, 500 K) are predicted for SrMgSi and CaMgGe, respectively. The theoretical study provides a valuable direction for exploring Zintl-phase materials for efficient TE power conversion

Comparisons of total yield and OVPUA of different planting patterns.

<p>MME  =  monoculture maize in even rows, MMW  =  monoculture maize in alternating wide and narrow rows, MA  =  alfalfa monoculture, IMA1  =  maize intercropped with one row of alfalfa in the wide rows, IMA2  =  maize intercropped with two rows of alfalfa in the wide rows. Values in the parentheses are yields based on the whole of the intercropping area, including the areas occupied by both maize and alfalfa, and are equal to the yields of maize or alfalfa divided by their respective area proportion. The intercropping area proportions of maize and alfalfa were respectively 76.9% and 23.1% in the IMA1 treatment, while the intercropping area ratios occupied by alfalfa and maize were 53.8% and 46.2% in the IMA2 treatment. Different letters in the same column following the values indicate significant difference between different cropping patterns, and * denotes significant difference between years (<i>P</i> <0.05). Value  =  mean ± S.</p><p>Comparisons of total yield and OVPUA of different planting patterns.</p

Monthly precipitation (bar) and air temperature (curve) of the experimental site in 2011 and 2013.

<p>Monthly precipitation (bar) and air temperature (curve) of the experimental site in 2011 and 2013.</p

Leaf area index comparisons of alfalfa under monoculture and intercropping (A) and at different flowering stages (B).

<p>Significant differences between different alfalfa flowering stages are indicated by lower case letters (<i>P</i> <0.05). The other symbols are the same as for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110556#pone-0110556-g002" target="_blank">Figure 2</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110556#pone-0110556-g004" target="_blank">4</a>.</p

Leaf area index comparisons of maize at the harvest stage under monoculture and intercropping.

<p>Significant differences between different cropping patterns are indicated by lower case letters (<i>P</i> <0.05). The other symbols are the same as for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110556#pone-0110556-g002" target="_blank">Figure 2</a>.</p

Results of repeated measures ANOVA on maize leaf area index (LAI) and yield, alfalfa yield and comprehensive benefit analysis of total yield and output value per unit area (OVPUA), with cropping pattern (CP) as the independent variable and year (Y) as the repeated measure.

<p>Df  =  degrees of freedom, ns  =  no significant difference, * <i>p</i> <0.05, ** <i>p</i> <0.01</p><p>Results of repeated measures ANOVA on maize leaf area index (LAI) and yield, alfalfa yield and comprehensive benefit analysis of total yield and output value per unit area (OVPUA), with cropping pattern (CP) as the independent variable and year (Y) as the repeated measure.</p

Soil water content comparisons of different cropping patterns in 2011 (A) and 2013 (B).

<p>The inset figures show the average soil water content in different planting patterns during the vegetation period. SWC  =  soil water content. The other symbols are the same as for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110556#pone-0110556-g002" target="_blank">Figure 2</a>.</p

Rational Design of Tetrahedral Derivatives as Efficient Light-Emitting Materials Based on “Super Atom” Perspective

Traditional semiconductor quantum dots of groups II–VI are key ingredients of next-generation display technology. Yet, the majority of them contain toxic heavy-metal elements, thus calling for alternative light-emitting materials. Herein, we have explored three novel categories of multicomponent compounds, namely, tetragonal II-III2-VI4 porous ternary compounds, cubic I2-II3-VI4 ternary compounds, and cubic I-II-III3-V4 quaternary compounds. This is achieved by judicious introduction of a “super atom” perspective and concurrently varying the solid-state lattice packing of involved super atoms or the population of surrounding counter cations. Based on first-principles calculations of 392 candidate materials with designed crystal structures, 53 highly stable materials have been screened. Strikingly, 34 of them are direct-bandgap semiconductors with emitting wavelengths covering the near-infrared and visible-light regions. This work provides a comprehensive database of highly efficient light-emitting materials, which may be of interest for a broad field of optoelectronic applications