|A block of Indium metal. (Source: periodictable.com.)|
Elements and Their Scarcity
For an overall perspective :
"There are two reasons for chemical elements to become scarce. Some ... are simply not that abundant anywhere in the Earth's crust, whereas others are found in only a few places, which might create political issues for their supply." A few examples are the following:
Rare-Earth Metal Neodymium [Nd]. This element is a key component of small, lightweight, strong, and permanent magnets used in emerging technologies from portable electronics to hybrid vehicles to wind turbines. King  has outlined approximate figures of 1 kg Nd used in every Toyota Prius and 300 kg Nd used in every wind turbine. As China mines 97% of the global rare-earth metal supply, they possess great control of the market price as well as quality of exported form (i.e. low-value raw ore or high-value finished products) . As King puts it, "if there is only one supplier there is always concern."
Tellurium [Te]. Cadmium Telluride [CdTe] solar cells are  "probably the highest-performing solar cells if you look at the cost per kilowatt." But Te is also essentially a by-product of copper mining, which complicates its acquisition. According to King, Te "is produced in such small quantities that the total value of copper produced by a mine completely outweighs the value of Tellurium. The Tellurium production is never going to drive a miner to open a mine."
Indium [In]. This element - more specifically, the compound Indium-Tin-Oxide (ITO) - is a key component in flat-panel displays, touch screens, and cell phones. In contrast to the rare-earth metals above, Indium is considered a truly rare metal with an estimated worldwide reserve base (2007) of 6,000 tonnes . Like Tellurium, Indium is obtained through mining of other materials such as Zinc  - and Canada produces a large percentage of the global volume (~33% ). But with rarity comes high and volatile prices (fluctuating between $300-$500 per kilogram) , which can cause great difficulty in securing a supply chain for a product.
Platinum [Pt]. This element has been used for some time as part of catalysts. With an estimated reserve base of 77,000 tonnes it is not quite as rare as Indium ; but the production of Platinum-group metals is concentrated primarily in South Africa [2,4], thus making unpredictable the cost of this metal.
Phosphorus [P]. Although a physically-abundant element, Phosphorus is also considered vulnerable because of its far-reaching inclusion in a wide range of materials and chemicals - specifically fertilizer. As outlined in , "a shortage of Phosphorus fertilizer would cause significant damage to agriculture, resulting in an immediate food crisis."
Identifying Materials Science Limitations and Solutions
As outlined in [1,2], Japan - a country consuming high volumes of scarce elements but without the ability to mine them - very early realized the problem of element shortages; Japan then spearheaded the development of an 'Element Strategy Initiative', which focuses on four key components: 1) substitution, 2) regulation, 3) reduction, and 4) recycling.
Materials science and engineering can achieve advances in these four components of this initiative, perhaps clearest in substitution, reduction, and recycling. First, new and less-scarce materials can be developed as alternatives to those described above. Outlined in , recent examples have shown that novel lime-alumina compounds can replace ITO in some functionality. Other recent work has focused on carbon-based replacements for ITO. Moreover, in some cases the supply of an element provides a hard limit to the reach of a new technology: for example, mining all the world's Platinum for automobile fuel cells would be able to produce less than 5% of the global car production . There are many examples of substitution-type materials science developments constantly on-going, each weighed against the current benchmarks in terms of performance, but also weight, cost, lifetime, stability, etc. But as King  points out, an exact swap is not likely to happen: instead, the re-design of the material will require the re-design of the product - a reiterative process which itself possesses considerable work.
Second, improved materials product development can help reduce required material volumes. In addition, increased efficiency of raw materials processing can help reduce front-end waste as well as enable mining from more low-grade sources . Third, increased focus on materials life-cycle design - "something that is really not yet done in any significant manner"  - can help return scarce materials to the supply chain. The potential value of this third component is considerable in some cases. In Japan, for example, there are what are called 'urban mines' consisting of discarded high-tech devices; in these 'mines', Nakamura and Sato  cite volumes of "6,800 tons of gold (16% of the world reserves), 60,000 tons of silver (22%), and 1,700 tons of indium (15.5%)..." In addition, as outlined in , "the use of rare earths in electronic gadgets has risen so much that their concentration in computers is actually higher than that in mines. It pays to recycle."
In short, while the context of the articles discussed focuses on scarcity, the same sentiments may be applied to even the most conventional and abundant materials. The supplies of all elements will change over time, as will their costs (both monetary and otherwise). In , it is thought that "eventually, market forces will of course even out such imbalances in supply and demand." And with each cycle or fluctuation :
"Instead of regarding this situation merely as a crisis to overcome, we should convert it to an opportunity to create a new materials science, new materials and a new industry."
 Elements in short supply (Editorial). Nature Materials, Vol. 10 (2011) p. 157.
 E. Nakamura and K. Sato. Managing the scarcity of chemical elements. Nature Materials, Vol. 10 (2011) pp. 158-161.
 Purveyor of the rare (Interview by J. Heber). Nature Materials, Vol. 10 (2011) pp. 162-163.
 D. Cohen. Earth audit. New Scientist, Vol. 194, Issue 2605 (2007) pp. 34-41.
 Mineral Commodity Summaries 2010. U.S. Geological Survey (2010) pp. 74-75. (Available On-Line.)