DEVELOPMENT, BY PRESSURE, OF POLAR ELECTRICITY IN HEMIHEDRAL CRYSTALS WITH INCLINED FACES. Pgs. 6-9
DEVELOPPEMENT, PAR PRESSION,
DE
L’ELECTRI CITE POLAIRE
DANS LES
CRISTAUX HEMIEDRESA FACES 1NCLINEES.
En commun avec JACQUES CURIE.
Comptes rendus de V Academic des Sciences, t. XC1, p. 294,
seance du 2 aout 1880.
DEVELOPMENT, BY PRESSURE,
OF
POLAR ELECTRICITY
IN
HEMIHEDRAL CRYSTALS WITH INCLINED FACES.
In collaboration with JACQUES CURIE.
Proceedings of the Academy of Sciences, vol. XC1, p. 294,
session of August 2, 1880.
1. Les cristaux possedant un ou plusieurs axes dont les extremites sont dissemblables, c’est-a-dire les cristaux hemiedres a faces inclinees, jouissent d’une propriete physique speciale, celle de donner naissance a deux poles electriques de noms contraires aux extre mites des axes susdits, lorsqu ils subissent nne variation de temperature : c’est le phenomene connu sous le nom d zpyroelectricite.
1. Crystals with one or more axes whose ends are dissimilar—that is, hemihedral crystals with inclined faces—possess a special physical property: when subjected to a change in temperature, they generate two electric poles with opposite charges at the ends of the aforementioned axes. This phenomenon is known as pyroelectricity.
IN oiis avons trouve un nouveau mode de developpement de Pelectricite polaire dans ces memes cristaux, qui consiste a les sournettre a des variations de pression suivant leurs axes d’liemiedrie ( 1 ).
(1) Bulletin de la Societe mineralogique, 1880.
We have discovered a new method for inducing polar electricity in these same crystals, which involves subjecting them to pressure variations along their axes of symmetry (1).
(1) Bulletin of the Mineralogical Society, 1880.
Les elfets produits sont entierement analogues a ceux causes par la chaleur : pendant une compression, les extremites de 1 axe sur lequel on agit se chargent d’electricites contraires; une lois le crista l ramene a Petal ne utre, si on le decomprime, le phenomene se reproduit, mais avec line inversion des signes; Pextremite qui se chargeait positivement par compression devient negative pen¬ dant la decompression, et reciproquement ( 1 ).
(1) Les cristaux hemiedres a faces inclinees soni les seuls cristaux pyroelectriques; ce sonl aussi les seuls capables d’acquerir 1’elecLriciie polaire par pression. Gerlains cristauv holoedres, comme le spath, se chargent bien par pression, mais d’une seule eleclricile; c’est la un phenomene de surface, enlierement dif¬ ferent, el dont retl'et eta i t insensible dans les conditions de nos experiences.
The effects produced are entirely analogous to those caused by heat: during compression, the ends of an axis on which a force is applied become charged with opposite electricities; once the crystal is returned to its original state, if it is decompressed, the phenomenon is reproduced, but with the signs reversed; The end that became positively charged during compression becomes negatively charged during decompression, and vice versa (1).
(1) Hemihedral crystals with inclined faces are the only pyroelectric crystals; they are also the only ones capable of acquiring polar electricity through pressure. Most holoedral crystals, such as spath [Iceland Spar or Calcite], do become charged by pressure, but with a single polarity; this is a surface phenomenon, entirely different, and to which the retl'et was insensitive under the conditions of our experiments.
Pour faire line experience, on tarlle deux faces paralleles entre dies et perpendiculaires a un axe d’hemiedrie clans la substance que bon vent etudier; on les revet cle deux feuilles d’etain qu’on isole exterieurement par deux plaques en caoutchouc clnrci; le tout etant place entre les machoires d’un etau, par exemple, on pent exercer des pressions sur les deux faces taillees, c’est-a-dire suivant Paxe d’hemiedrie lui-meme. Pour constater Pelectrieite, nous nous sommes servis d’un electrometre Thomson. On peut montrer la difference de tension des extremites en mettant chaque feuille d’etain en communication avec deux des couples de secteurs de 1 instrument, l’aiguille etant chargee cl’une electncite connue. On peut aussi recueillir separement chacune des electricites; il suffit pour cela de mettre une des feuilles d’etain en com¬ munication avec la terre, l’autre etant en communication avec l’aiguille et les deux couples de secteurs etant charges a Paide cl’une pile.
Quoique n’avant pas encore aborde 1 etude des lois qui regissent le phenomene, nous pouvons dire qu’d presente des caracteres identiques a ceux de la pyroelectricite tels cjue les a delinis Gaugain dans son beau travail sur la tourmaline.
To perform this experiment, two parallel faces are cut between dies and perpendicular to a half-axis within the material under study; these are covered with two sheets of tin, which are insulated on the outside by two circular rubber plates; with the whole assembly placed between the jaws of a vise, for example, pressure can be applied to the two cut faces, that is, along the axis of the hemidire itself. To observe the electrostatic charge, we used a Thomson electrometer. The difference in voltage at the ends can be demonstrated by connecting each tin foil to two of the instrument’s sector pairs, with the needle charged to a known potential. One can also collect each of the electricities separately; to do this, simply connect one of the tin foils to ground, while the other is connected to the needle, and the two pairs of sectors are charged by a battery.
Although we have not yet undertaken a study of the laws governing this phenomenon, we can say that it exhibits characteristics identical to those of pyroelectricity, as described by Gaugain in his excellent work on tourmaline.
2. Nous avons fait l’etude comparee des deux modes de developpement d’electricite polaire sur une serie de substances non conductrices, hemiedres a faces inclinees, qui comprend a peu pres Unites celles qui sont connues comme pyroelectriques (2).
(2) On peut prevo'r qu’il en existe beaucoup d’aulres parmi les substances cristallisees art ificielles. Les corps actifs sur la lumiere polarisee, par exemple, fournissent des cristaux dont certains diametres ont leurs extremites dissemblables.
Inaction de la chaleur a ete etudiee a l’aide du procede indique par M. Friedel, procede qui est d une si grande commodite (').
(') Bulletin de la Societe mineralogique, 1879.
2. We have conducted a comparative study of the two modes of polar electricity generation on a series of non-conductive substances, hemispheres with inclined faces, which includes nearly all those known to be pyroelectric (2).
(2) It can be anticipated that there are many others among artificial crystalline substances. Substances active in response to polarized light, for example, yield crystals in which certain faces have dissimilar ends.
The effect of heat was studied using the method described by Mr. Friedel, a method of great convenience (').
(') Bulletin of the Mineralogical Society, 1879.
Nos experiences ont porle sur la blende, le chlorate de sonde, la boracite, la tourmaline, le quartz, la calamine, la topaze, l’acide tartriqne droit, le sucre, le sel de Seignette.
Pour tons ces cristaux, les elFets produits par compression sont de meme sens que ceux produits par refroidissement; ceux dus a une decompression sont de meme sens que ceux dus a un echauffement.
11 j a la une relation evidente qui permet de rapporter dans les deux cas le phenomene a une cause unique et de les reunir dans l’enonce suivant :
Quelle que soit la cause determinante, toutes les fois qu un cristal hemiedre a faces inclinees , non conducteur , se con¬ tracted il y a formation de poles electriques dans un certain sens; toutes les fois que ce cristal se dilate , le degagement d’ electricite a lieu en sens contraire.
Our experiments focused on blende, sodium chlorate, boracite, tourmaline, quartz, calamine, topaz, anhydrous tartaric acid, sugar, and Seignette’s salt [Rochelle salt]. For all these crystals, the effects produced by compression are of the same nature as those produced by cooling; those due to decompression are of the same nature as those due to heating. There is an obvious relationship that allows us to attribute the phenomenon in both cases to a single cause and to summarize them in the following statement:
Whatever the determining cause, whenever a non-conductive hemihedral crystal with inclined faces contracts, electric poles are formed in a certain direction; whenever this crystal expands, the release of electricity occurs in the opposite direction.
Ge procede de Friedel consiste a prendre une lame cristalline taillee perpendiculairement a un axe d’hemiedrie (axe non double) sur une face de laquelle on applique une demi-spliere de laiton chaufTee. II en resulte une polarisation electrique de la lame et une deviation de l’electromelre auquel la demi-spliere est reliee. La pyroelectricite ainsi definie et dont il est question dans les Notes de P et J. Curie n’est pas celle que Ton considere habituellement et qui consiste dans la polarisation electrique d’un cristal par variation uniforme de la temperature dans sa masse; ce dernier phenomene se manifeste uniquement dans les cristaux hemimorphes qui ne presentent, comme la tourmaline, qu'un seul axe de symetrie.
Friedel’s method consists of taking a crystal slab cut perpendicular to a hemidirexional axis (a non-double axis), to one face of which a heated brass half-spire is applied. This results in the electrical polarization of the slab and a deflection of the electrometer to which the half-spire is connected. The pyroelectricity thus defined, and discussed in the Notes by P. and J. Curie, is not the one usually considered, which consists in the electrical polarization of a crystal due to a uniform variation in temperature within its mass; this latter phenomenon occurs only in hemimorphic crystals which, like tourmaline, have only a single axis of symmetry.
Le phenomene observe par Friedel est en realite piezoelectriq ue et resulte des compressions produites dans le cristal par l’echauffement non uniforme du a la demi-sphere metallique. La decouverte ulterieure de la piezo electricite en a fourni l’explication et Friedel en a lui-meme reconnu la vraie nature dans une Note publiee en commun avec J. Curie et dont voici les conclusions :
The phenomenon observed by Friedel is in fact piezoelectric and results from the compressions produced in the crystal by the non-uniform heating caused by the metal hemisphere. The subsequent discovery of piezoelectricity provided an explanation for this, and Friedel himself acknowledged its true nature in a note published jointly with J. Curie, the conclusions of which are as follows:
« Nous pensons pouvoir conclure de ces faits d’une maniere generale que dans les substances hexagonales ayant trois axes horizontaux d’hemimorphisme et dans les substances cubiques appartenant au mode d’hemiedrie tetraedrique, orsqu’il y a echaulTement ou refroidissement regulier du cristal, c'est-a-dire lorsque les dilatations sont egales par rapport aux dilTerents axes en question, il y a compensation au point de vue pyroelectrique et l’on n’observe aucun degage¬ ment d’electricile. On en obtiendra au contraire lorsqu’une variation irreguliere de la temperature ou une compression interessant certains axes plus que d’autres produira des dilatations inegales. » (C. Friedel et J. Curie, Comptes rendus de VAcademie des Sciences, t. XCVII, 1 883 , p. 66.) [ iXotes des Edileurs.}
Si cette maniere de voir est exacte, les effets dus a la compres¬ sion doivent etre de meme sens que ceux dus a l’echauffement dans une substance possedant suivant l’axe d’hemiedrie un co effi¬ cient de dilatation negatif (1).
(1) Ge travail a ete fait au laboratoire de Mineralogie de la Faculte des Sciences.
"We believe we can generally conclude from these facts that in hexagonal substances with three horizontal axes of hemimorphism and in cubic substances belonging to the tetrahedral hemiedry mode, when there is uniform heating or cooling of the crystal—that is, when the expansions are equal with respect to the various axes in question— there is compensation from a pyroelectric standpoint, and no release of electricity is observed. On the contrary, it will occur when an irregular variation in temperature or a compression affecting certain axes more than others produces unequal expansions. ” (C. Friedel and J. Curie, Comptes rendus de l’Académie des Sciences, vol. XCVII, 1883, p. 66.) [Editors’ notes.]
If this view is correct, the effects due to compression must be of the same nature as those due to heating in a substance possessing, along the semi-axial axis, a negative coefficient of expansion (1).
(1) This work was carried out at the Mineralogy Laboratory of the Faculty of Sciences
SUMMARY - NOTES:
Hemidire / Hemidirexional: In the original French, they likely used hémièdre or axe d'hémiédrie. In English crystallography, we use Hemihedral axis or Axis of hemihedry.
In 1880, brothers Pierre and Jacques Curie discovered that certain types of crystals can produce electricity simply by being squeezed. Before this, scientists knew that heating some crystals could create an electric charge (a process called pyroelectricity). The Curies proved that mechanical pressure does the exact same thing.
How it works:
The Squeeze: When you compress these specific crystals along a certain "axis" (direction), one end becomes positively charged and the other becomes negatively charged.
The Release: When you stop squeezing and let the crystal expand back to its original shape, the charges appear again, but they flip—the positive end becomes negative and vice versa.
The Rule: The Curies discovered a simple law: Contraction (shrinking) always produces one type of charge, while Expansion (growing) always produces the opposite, regardless of whether that change was caused by cold or by physical pressure.
Why it matters: Not all crystals can do this. It only happens in "hemihedral" crystals—those that are naturally asymmetrical. This discovery revealed a deep link between the physical structure of matter (its shape) and its electrical properties.
Today, we call this the Piezoelectric Effect. It is the reason a "quartz" watch keeps time (electricity makes the crystal vibrate) and how an electric grill starter creates a spark (a tiny hammer hits a crystal to create a high-voltage charge).
