Why is the thermoelectric figure of merit denoted by $ZT$?

Question

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 $Z$.

@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. — , Oct 26 '16 at 07:11
I guess because German Physicists were very much involved in the foundations of Thermodynamics.. — , Oct 26 '16 at 07:50

score 2 · Answer 1 · answered Oct 26 '16 at 07:36

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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.

answered Oct 26 '16 at 07:36

John Rennie

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In that book, it is just denoted as a lowercase "z", rather than the uppercase "ZT". – Oct 27 '16 at 06:06
While according to Goldsmid, H. J. Introduction to Thermoelectricity, Springer-Verlag Berlin Heidelberg, 2016, "ZT" is dimensionless, and "T" there means temperature. – Αλέξανδρος Ζεγγ Oct 27 '16 at 06:16
@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. – John Rennie Oct 27 '16 at 06:23
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. – Gerald Edgar Oct 27 '16 at 15:03
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. – user58697 Oct 28 '16 at 03:10
@GeraldEdgar Yes, that is true. – Αλέξανδρος Ζεγγ Oct 29 '16 at 07:59
@user58697 Thanks for providing the information about Russian! – Αλέξανδρος Ζεγγ Oct 29 '16 at 08:00

score 2 · Answer 2 · answered Oct 29 '16 at 14:57

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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]

answered Oct 29 '16 at 14:57

Gerald Edgar

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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.) – Janosh Jan 21 '19 at 14:06

Why is the thermoelectric figure of merit denoted by $ZT$?

2 Answers2