Diamond-anvil cell (DAC) provides opportunity to explore the new insight of material science under extreme high pressure. In particular, DAC combined with laser heating system is a powerful tool for synthesizing novel materials. In this article, we review the recent advanced researches on the synthesis of novel metal nitride and the crystal growth of rectangular hollow tube oxides by means of the high-pressure experiments using laser-heated diamond anvil cell.
High-pressure synthesis, crystal structure, and physical properties of mercury-containing transition-metal oxides were introduced from a viewpoint of coordination chemistry of mercury. It is interesting that mercury behaves not only as a cation (Hg2+) but also as a molecule anion (HgO22−) and metal cluster (Hgn). Since mercury is volatile, high-pressure synthesis is an essential technique to produce new mercury-containing compounds.
In this article, I introduced some new metallic germanides with electropositive elements. Those compounds have covalent Ge networks such as a three dimensional tunnel structure (LaGe5), one dimensional chains of face-shared elongated Ge6 octahedra (BaGe3), and discrete Ge3 triangle units (LaGe3). The germanides showed some characteristics of Zintl type compounds, but the electrical resistivity measurements revealed that they were metallic. I made a comparison between those metallic compounds and classical Zintl phases. The electronic structures of the metallic germanides were discussed in terms of the orbital interaction between host (germanium) and guest (electropositive elements) atoms.
Compounds with the postperovskite (PPv)-type crystal structure were searched using a Kawai-type multi-anvil high-pressure apparatus. We succeeded in synthesizing PPv-type CaRuO3, CaRhO3, NaNiF3, NaCoF3, and NaZnF3 and found that perovskite (Pv)-type NaMnF3 decomposes into two phases above about 10 GPa instead of phase transition to a PPv phase. The PPv-type CaRuO3, CaRhO3 and NaNiF3 are quenchable without partial back-transformation to the Pv-type structure. The structure refinements of the synthesized compounds suggest that PPv-type NaNiF3 and NaZnF3 are preferable to the other PPv-type compounds as analogue materials of PPv-type MgSiO3 which is accepted as a major constituent mineral in the Earth's lowermost mantle.
Recent studies in our group on high-pressure synthesis of perovskite-related compounds with polar structure, their structures and functional properties were reviewed. First, the experimental procedures for high-pressure synthesis using cubic multi-anvil apparatus, and synthesis under an oxygen pressure of approximately 10 atm using a sealed glass tube were explained. Next, the high pressure synthesis of various LiNbO3-type oxides with polar structure such as ZnMO3(M=Ti, Sn), MnMO3(M=Ti, Sn), PbNiO3 as well as an A-site ordered perovskite ferroelectrics CaMnTi2O6 and their functional properties were described. Finally, the possibility of high-pressure synthesis of inorganic materials in the future was mentioned.
Hydrothermal synthesis, which is a type of the high-pressure syntheses, has been known as a useful method for single-crystal growth. We utilize this method for searching novel materials. In the beginning of this article, we give a brief explanation about the method. Next we report the crystal structures and exotic magnetic properties of several novel compounds that we discovered. We also show our attempts to obtain pure single crystals of several natural minerals which exhibit interesting magnetism arising from the geometric frustration.