High pressure synthesis of ammonium tungsten bronze superconducting phases from a molecular solid acid H3PW12O40·nH2O (n ∼28) in BN crucibles
High pressure synthesis of ammonium tungsten bronze superconducting phases from a molecular solid acid H3PW12O40·nH2O (n ∼28) in BN crucibles
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DOI：
10.1016/j.jallcom.2008.03.116
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发表时间：
2009-02
影响因子：
6.2
通讯作者：
Atsushi Anzai;K. Inumaru;S. Yamanaka
中科院分区：
文献类型：
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作者：
Atsushi Anzai;K. Inumaru;S. Yamanaka
多金属氧酸盐分子化合物H3PW12O40·nH2O(n∼28)在高压高温条件下(10 Gpa，873-1173K)在BN坩埚中进行了处理。粉末X-射线衍射、电子探针分析和红外吸收光谱证实了产物为(NH_4)_xWO_3(x-∼为0.26-0.34)。当原料在BN槽中在常压下加热时，不会形成这种化合物，这表明高压承压水分子在体系中存在，并在酸存在的情况下导致BN坩埚壁上的水解反应，从而在槽中生成铵离子。在973K下形成的(NH4)0.25WO_3产物在5.2K以下表现出超导电性，这是文献报道的钨青铜铵相的最高转变温度。
A polyoxometalate molecular compound H3PW12O40·nH2O (n ∼28) was treated under high pressure and high temperature conditions (10GPa, 873–1173K) in BN crucibles. Powder X-ray diffraction, electron microprobe analysis, and infrared absorption spectroscopy confirmed the formation of (NH4)xWO3(x ∼0.26–0.34) as the main product. This compound was not formed when the source material was heated at ambient pressures in a BN cell, suggesting that the high pressure confined water molecules in the system and brought about the hydrolysis reaction on the BN crucible walls in the presence of the acid to generate ammonium cations in the cell. The (NH4)0.25WO3product formed at 973K showed superconductivity below 5.2K, which is the highest transition temperature in ammonium tungsten bronze phases reported in the literature.