There is at least the Kondo effect for generic metals with magnetic impurities. The resistance increases with T->0 and becomes arbitrarily large. Of course this is very different from an insulator with a band-gap.

Thanks Christian Binek. It is an useful information. However, I am looking for a information if any metal (elemental) or their alloy has been found to become insulator on cooling towards T = 0.

I do not know any example of a metallic to insulating behaviour if there is no associated phase change. For example liquid germanium and silicon are metallic while solid Ge and Si are semiconducting. A phase change may change the electronic band structure allowing this kind of transition in the electronic transport properties. It is difficult to understand how with a given DOS a metal can become insulating by cooling. By heating it is different. Pressure increases the metallicity while temperature decrease it. The temperature increases the distance between atoms, thus electrons become localised.

Superconductors may be thought to be candidate. The generic phase diagram of high Tc superconducting materials tell us that depending on the carrier concentration it may show both metallic and insulating behavior as a function of temperature.

Thanks Jean-Georges, I too thought so but was not sure, somehow. I appreciate your comment which rightly asked me to think on, - how a metal of given DOS can become insulator just by cooling ? However, your argument that "The temperature increases ... .... electrons become localised" seems to indicate that a metal can become insulator by increasing temperature. Is this inference of mine right ? Is there any such example ? Please comment. Apparently, localisation is possible with decrease in kinetic energy, hence not by increase in temperature. So far I understood that resistance of a metal increases with increase in temperature because of increasing probability of electron collision with lattice, etc.

Thanks Ugur Topal.

The Bechgaard salts are an example. They are charge transfer metals at high temperature and as 1-D chains as they cool they undergo a peierls transition, double the unit cell and become an insulator. Many, many materials undergo an ordering transition at low temperature and behave as semiconductors/insulators.

Most extrinsicly doped semiconductors have thermaly excited conduction electrons at high temperatures showing metallic resistivity and then a low temperatures become insulators.

Fig 2, 3 and 4 of my paper : "Understanding the resistivity and absolute

thermoelectric power of disordered metals and alloys" explain it. We have to compare the energy of the electrons at the Fermi energy which are those implied in the conductivity, to the total potential. If the distance increases, the energy E (relative to the potential barrier) decreases and becomes negative. The electrons can no more cross the potential barrier and become localised. An example of it are the "expended metals" (Hensel in Marburg). There is a competition between pressure and temperature and we have resistivities varying following what I have explained above.

Changing the nature of a metal is somehow strange: maybe it wouldn't be a metal anymore. But maybe a degenerated semiconductor (not a metal but somehow acting as one) for the right concentration of impurities would change to a semiconductor and then to insulator as temperature decreases.

I found amorphous Ni-Nb-Zr-H alloys that become an insulator upon cooling.

I attached two references

Prof. Dr. Mikio Fukuhara

Research Institute for Electromagnetic Materials

Tohoku University

I found amorphous Ni-Nb-Zr-H alloys that become an insulator upon cooling.

I attaced references

Prof. Dr. Mikio Fukuhara

Research Institute for Electromagnetic Materials

Tohoku University

@Mikio Fukuhara, It appears that you somehow missed to attach the references

Attachnent system can't send one file only. I send two ones later

2nd one

3rd one. Please refer other ones from Ref. of the 1st one.

Fesi

Fesi

FeSi (iron monosilicide)

FeSi is a narrow band-gap semiconductor at RT but it becomes metallic (bad metal though) at low temperature. So that is not what Jatendra was looking for. Mikio's sampple is probably is more relevant.

FeSi is a narrow band-gap semiconductor at low T, exhibiting variable-range hopping conduction. At room T the gap disappears and FeSi become a metal. See attached file and references therein.

I checked it. Yes, you are right.

@Konstantin and Jatendra: I am sorry for giving wrong information on FeSi. But of course Jatendra was looking for metallic elements or alloys and FeSi is neither of it. There are many other examples of such metal-insulator transitions but they are also not a metallic element or alloy.

I can think of a number of cases that might be of interest

(i) systems with instabilities (e.g. Peierls, CDW type), where new gaps [edit: in the band structure] open below some characteristic **temperature** (typo was: band structure). However, an appropriately calculated band structure (which in the vast majority of cases corrensponds to a T=0 calculation) would yield an insulating groud state from the outset.

(ii) correlated materials in general

Naive band calculations would expect materials like CoO to be metals due to partial d-shall filling. It has been a major development to produce calculations that correctly predict the insulating state (due to Coulomb correlations) even though our understanding of the mechanism was shaped by N. Mott many years ago.

(iii) Kondo insulators, again an effect due to correlations,

@Tapan, why shouldn't an alloy containing Si not be a metallic alloy? Just because elemental Si happens to be an insulator?

Edited due to errors. Sorry for those!!

Thanks to all experts who contributed to this question and who have been following it. I would still be looking for newer information, so please help me to get more examples.

I take this opportunity to wish you all a very happy new year 2014.

PrRu4P12 with Skutterudite Structure is a metal at 300 K and show Metal-insulator transition at around 60 K without a structural phase transition

http://prl.aps.org/pdf/PRL/v79/i17/p3218_1

Dear Yatendra Jain, would you mind being more specific about what kind of examples you're thinking at and what kind of information would qualify as "newer" with you?

Dear Dr Kai, I have developed a theoretical framework that I can use to explain the superfluidity of liquid $^4$He type systems of interacting bosons and equally well the superconductivity/superfluidity of electron fluid and liquid $^3$He type systems of interacting fermions using macro-orbital representation of a constituent particle rather than a plane wave representation. Macro-orbital representation helps us in developing the many body theory in the framework of FIRST QUANTIZATION. A macro-orbital identifies each particle as a part or representative of a pair of particles moving with equal and opposite momenta (q,-q) with respect to the centre of mass of the pair which moves with momentum $K$ in the laboratory frame. This representation is a consequence of the wave superposition of quantum particles in the low temperature state of the system and this can not be avoided because constituent particles are quantum particles which have wave particle duality. Recently I was analysing the electron fluid of a conductor in this frame work further and I found that there are three possibilities one the electron fluid becomes superconducting below certain $T$, second the electron fluid remain as normal as at high $T$ and the conductor remain normal conductor even at $T=0$, and third the electrons of electron fluid get localised at certain $T$ and conductor becomes insulator on cooling. It is in this context that I was looking for examples of metals that become insulators. I hope this makes my question reasonably specific and clear. I am thankful to all people who have contributed to this question and have greatly helped me in my endeavour. I appreciate your observation which helped me to clarify my question.

Thanks!!

I think what Yatendra means is an alloy material where each of its individual elements are metals. This is clearly not the case for oxygen or Si. The questions still holds ¿are there any reported metal alloys that have insulating properties at any temperature?

Silicon and germanium are metallic in the liquid state and become semi-conductors when they solidify. In this case it correspond to a change of phase.

In the liquid state CdTe is semiconducting near the melting point and becomes more metallic at higher temperature. It is the same thing with Zn-Sb, Se-Te; Th_Te... The gap is closening with temperature (opening when you cool). One can probably expect that it is the same thing with metallic semi conductors (Half Heussler alloys).