Why is the thermoelectric figure of merit denoted by $Z T$? Does $Z T$ come from the abbreviation of words in some language?

Update: So far, $T$ has been figured out — it is the temperature, to make the whole quantity dimensionless. So, the question is left only for $Z$.

  • 1
    $\begingroup$ Possibly German? $\endgroup$
    – Farcher
    Commented Oct 26, 2016 at 6:29
  • $\begingroup$ @Farcher I do not think so. According to Google translation, thermoelektrischen Gütefaktor is corresponding to thermoelectric figure of merit --- the letter "Z" does not even appear in the German word. $\endgroup$
    – Alexander Zeng
    Commented Oct 26, 2016 at 7:11
  • $\begingroup$ I guess because German Physicists were very much involved in the foundations of Thermodynamics.. $\endgroup$
    – Farcher
    Commented Oct 26, 2016 at 7:50

2 Answers 2


The concept of the thermoelectric figure of merit and the abbreviation ZT were introduced by the Russian physicist Abram Fedorovich Ioffe in 1949, so I assume the acronym originates from Russian. However all the references I can find are behind paywalls so frustratingly I cannot tell you how ZT is derived.

If your university has access to it, Ioffe's book where all this is described is Ioffe AF (1957) Semiconductor thermoelements, and Thermoelectric cooling.

  • $\begingroup$ In that book, it is just denoted as a lowercase "z", rather than the uppercase "ZT". $\endgroup$
    – Alexander Zeng
    Commented Oct 27, 2016 at 6:06
  • $\begingroup$ While according to Goldsmid, H. J. Introduction to Thermoelectricity, Springer-Verlag Berlin Heidelberg, 2016, "ZT" is dimensionless, and "T" there means temperature. $\endgroup$ Commented Oct 27, 2016 at 6:16
  • $\begingroup$ @AlexanderZeng: I've seen it as both zT and ZT. I don't know how Ioffe used it because I don't have access to his papers. $\endgroup$ Commented Oct 27, 2016 at 6:23
  • $\begingroup$ So the point is, you take the original figure of merit $Z$ and multiply by tempurature $T$ to make it dimensionless. The result is $ZT$. So half the answer is "$T$ stands for tempurature". Now we just need to know where $Z$ comes from. $\endgroup$ Commented Oct 27, 2016 at 15:03
  • $\begingroup$ It cannot be a Russian acronym. In Russian a "thermoelectric figure of merit" is "термоэлектрическая добротность". Nothing resembles Z or З, neither graphically nor phonetically. $\endgroup$
    – user58697
    Commented Oct 28, 2016 at 3:10

My guess for the Z

From THIS Germain-English dictionary, we see that "Figure of merit" in German could be

Gütezahl $\qquad$ or $\qquad$ Leistungskennzahl

in electrical engineering. So probably the letter Z is for Zahl, the German word for "number".

[moral: use Google translate with a grain of salt]

  • $\begingroup$ This seems plausible. Just wanted to add that the Z might also come from the word Ziffer (as in thermoelektrische Kennziffer which translates to thermoelectric indicator). Ziffer is a synonym for Zahl that is perhaps more frequently used in the sciences and engineering. (Disclaimer: I'm German.) $\endgroup$
    – Janosh
    Commented Jan 21, 2019 at 14:06

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