每周分子 | Molecule of the Week

Original ACS 美国化学会 ACS美国化学会 2022-07-01

每周分子: 二氧化钒

Molecule of the Week: Vanadium dioxide

二氧化钒 [钒（IV）氧化物（VO₂）]是钒的四种相对常见的氧化物之一。其他的是：

· 一氧化钒 [钒氧化物(VO)]；

· 三氧化二钒或三氧化二钒 [氧化钒(III),V₂O₃]；和

· 五氧化二钒 [ 氧化钒(V), V₂O₅]。

另外，存在几种混合的钒氧化物(主要存在于自然界中)，如V₃O₇ (VO₂ + V₂O₅)和V₄O₇ (2VO₂ + V₂O₃)。各种各样的钒氧化物在颜色、晶体结构和化学性质方面差异很大。

VO₂本身有时表示为V₂O₄, V₄O₈或其他V_nO_2n分子式，具体取决于其晶体的对称性。在低于67ºC的温度下，VO₂ 具有单斜晶体结构(如图所示)。当加热到67ºC以上时，它将转变为四方结构。在相同温度下，晶体VO₂ 从电绝缘体转换为导体。

但是，还有更多其他现象：2013年，由中野正树(Masaki Nakano)带领的来自the RIKEN Center for Emergent MatterScience(Wako)和东北大学(均在日本)的一个团队发现了绝缘子-导体现象会影响通过VO₂ 玻璃的光传输。以前已经证明，低温(<30ºC) VO₂ 玻璃对于红外(IR)辐射是透明的，但是在>60ºC时，它会反射IR光。中野等人通过将外部电压施加到VO₂ 薄膜上可达到相同的结果。这一发现是新型晶体管场效应的基础。

更重要的是：2017年，美国橡树岭国家实验室(位于美国田纳西州)和杜克大学的(位于美国北卡罗来纳州达勒姆)OlivierDelaire、美国加州大学伯克利分校和劳伦斯伯克利国家实验室的Junqiao Wu及全球的同行们表明，VO₂违反了古老的Wiedemann-Franz法则(1853年制定)，该法则认为金属的热导率的电子成分与其电导率之比与金属的温度成正比。在绝缘体--导体的转变温度及其以下，电子热导率异常低，这组作者指出，“这是强相关电子流体中热量和电荷独立扩散的准粒子不存在的标志。”

二氧化钒的下一个科学发现会是什么呢?

二氧化钒信息速览

CAS 登记号.	12036-21-4
SciFinder 命名	Vanadium oxide (VO₂)
分子式	O₂V
摩尔质量	82.94g/mol
外观	深蓝，黑或者灰色晶体或者粉末
熔点	1967 ºC
水溶性	不溶

二氧化钒信息速览危害信息

危害等级*	危害说明
口服，急性毒性，类别4	H302—吞咽有害
皮肤腐蚀/刺激，类别2	H315—引起皮肤刺激
严重眼损伤/眼睛刺激，类别2A	H319—引起严重眼刺激
急性毒性，吸入，类别4	H332—吸入有害
特定目标器官毒性，单次接触，呼吸道刺激，类别3	H335—可能引起呼吸道刺激

【关于每周分子】

自2001年以来，“每周分子”已成为广受欢迎的栏目。多数分子由读者推荐。每个结构都经由科学家审查，并以3-D和平面图像的形式显示，同时附有该分子简介。可以通过美国化学文摘社 (CAS) 提供的SciFinder中的CAS REGISTRY获取“每周分子”的更多信息。CAS REGISTRY中的每条物质信息都展示了物质的CAS登记号、索引名、通用名、商品名、书目信息等其他更多信息。发送邮件至motw@acs.org推荐您感兴趣的分子吧。

Vanadium dioxide [vanadium(IV) oxide, (VO₂)] is one of four relatively common oxides of vanadium. Others are

vanadium monoxide [vanadium(II) oxide, VO];
anadium sesquioxide or trioxide [vanadium(III) oxide, V2O3]; and
vanadium pentoxide [vanadium(V) oxide, V2O5].

In addition, several mixed vanadium oxides exist, many in nature. Examples are V₃O₇ (VO₂ + V₂O₅) and V₄O₇ (2VO₂ + V₂O₃). The vast range of vanadium oxides differ widely in terms of color, crystal structure, and chemical properties.

VO₂ itself is sometimes expressed as V₂O₄, V₄O₈, or other V_nO_2n formulas, depending on its crystalline symmetry. At temperatures less than 67 ºC, VO₂ has a monoclinic crystal structure (shown). When heated to more than 67 ºC, it transitions to a tetragonal structure. At the same temperature, crystalline VO₂ converts from an electrical insulator to a conductor.

But wait, there’s more: In 2013, a team led by Masaki Nakano at the RIKEN Center for Emergent Matter Science (Wako) and Tohoku University (both in Japan) built on the insulator–conductor phenomenon to affect light transmission through VO₂ glass. It had previously been shown that low-temperature (<30 ºC) VO₂ glass is transparent to infrared (IR) radiation, but at >60 ºC, it reflects IR light. Nakano et al. accomplished the same result by applying an external voltage to a thin film of VO₂. This discovery is the basis of new field-effect transistors.

And still more: In 2017, Olivier Delaire at the Oak Ridge National Laboratory (TN) and Duke University (Durham, NC); Junqiao Wu at the University of California, Berkeley, and Lawrence Berkeley National Laboratory; and colleagues worldwide showed that VO₂ violates the venerable (1853) Wiedemann–Franz law, which holds that the ratio of the electronic component of the thermal conductivity of a metal to its electrical conductivity is proportional to the metal’s temperature. At and below the insulator–conductor transition temperature, the electronic thermal conductivity is anomalously low, which, the authors state, “is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently."

What will scientists discover next about VO₂?

Vanadium dioxide fast facts

CAS Reg. No.	12036-21-4
SciFinder nomenclature	Vanadium oxide (VO₂)
Empirical formula	O₂V
Molar mass	82.94 g/mol
Appearance	Dark blue, black, or gray crystals or powder
Melting point	1967 ºC
Water solubility	Insoluble

Vanadium dioxide hazard information

Hazard class*	Hazard statement
Acute toxicity, oral, category 4	H302—Harmful if swallowed
Skin corrosion/irritation, category 2	H315—Causes skin irritation
Serious eye damage/eye irritation, category 2A	H319—Causes serious eye irritation
Acute toxicity, inhalation, category 4	H332—Harmful if inhaled
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3	H335—May cause respiratory irritation

*Safety data sheets vary widely; some state that VO₂ is not classified or is not a hazardous substance.
**Globally Harmonized System of Classification and Labeling of Chemicals.
Explanation of pictograms.

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