chemistry

Sodium tungsten bronze

Sodium tungsten bronze is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sodium tungsten bronze rather than just read about it. In short: Sodium tungsten bronze is a form of insertion compound with the formula NaxWO3, where x is equal to or less than 1. So named because of its metallic lustre, its electrical properties range from semiconducting to metallic depending on the concentration of sodium ions present; it can also exhibit superconductivity.

Key takeaways

Sodium tungsten bronze belongs to chemistry; place it in that map before memorising details.
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Connect Sodium tungsten bronze to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sodium tungsten bronze from memory before moving on to harder problems.

Reference excerpt

Sodium tungsten bronze is a form of insertion compound with the formula NaxWO3, where x is equal to or less than 1. So named because of its metallic lustre, its electrical properties range from semiconducting to metallic depending on the concentration of sodium ions present; it can also exhibit superconductivity.

History Prepared in 1823 by the chemist Friedrich Wöhler, sodium tungsten bronze was the first alkali metal bronze to be discovered. Tungsten bronzes owe some of their properties to the relative stability of the tungsten(V) cation that is formed. A similar family of molybdenum bronzes may have been discovered in 1885 by Alfred Stavenhagen and E. Engels, but they are formed in a very narrow range of temperatures and were not reported again until the 1960s.

Properties Sodium tungsten bronze, like other tungsten bronzes, is resistant to chemical reaction under both acidic and basic conditions. Colour is dependent upon the proportion of sodium in the compound, ranging from golden at x ≈ 0.9, through red, orange and deep purple, to blue-black when x ≈ 0.3. The electrical resistivity of the bronze depends on the proportion of sodium in the compound, with specific resistances of 1.66 mΩ being measured for some samples. It has been suggested that electrons, released when the sodium atoms are ionised, are conducted readily through the tungsten t2g and oxygen π orbitals. This can be observed in the XPS and UPS spectra: the peak representing the tungsten 5d band becomes more intense as x rises. For values of x below 0.3, the bronze is semiconducting rather than metallic. When cooled sufficiently, sodium tungsten bronze becomes a superconductor, with the critical temperature (Tc) for Na0.23WO3 being approximately 2.2 kelvin. The first record of superconductivity in a tungsten bronze was in 1964, with a Tc of 0.57 K.

Structure

When x = 1, sodium tungsten bronze adopts a cubic phase: the perovskite crystal structure. In this form, the structure consists of corner-sharing WO6 octahedra with sodium ions in the interstitial gaps. For x values between 0.9 and 0.3, the structure remains similar but with an increasing deficiency of sodium ions and a smaller lattice parameter. A number of other structure types can also be adopted, with varying electrical properties: cubic, tetragonal I and hexagonal phases are metallic, whereas orthorhombic and tetragonal II structures are semiconducting.

Synthesis Wöhler's 1823 synthesis involved reducing sodium tungstate and tungsten trioxide with hydrogen gas at red heat. A more modern approach reduces a melt of the reactants with electricity rather than with hydrogen. Microwave synthesis is also possible, using tungsten powder as the reducing agent. Hydrothermal (both batch and flow) syntheses are also possible.

Related compounds The sodium in this compound can be replaced by other alkali metals to form their tungsten bronzes, and by other metals such as tin and lead. Molybdenum bronzes also exist but are less stable than their tungsten counterparts.

References

Illustrations

Worked examples

Example 1 — a first encounter with Sodium tungsten bronze

Start with the simplest possible case. Write down what Sodium tungsten bronze claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sodium tungsten bronze before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sodium tungsten bronze ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sodium tungsten bronze

In research: Sodium tungsten bronze appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sodium tungsten bronze in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sodium tungsten bronze is common in secondary-school and first-year university syllabi. It links to neighbouring topics Non-stoichiometric compounds, Oxides, Sodium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Sodium tungsten bronze outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sodium tungsten bronze in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sodium tungsten bronze means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Sodium tungsten bronze in simple terms?

Why does Sodium tungsten bronze matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sodium tungsten bronze?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sodium tungsten bronze.